Patent Publication Number: US-2021180896-A1

Title: Firearm

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 16/433,941 titled “Firearm With Forward Charging System” filed Jun. 6, 2019, which is incorporated herein by reference in its entirety. The U.S. patent application Ser. No. 16/433,941 is a continuation of U.S. patent application Ser. No. 15/863,856 titled “Firearm With Forward Charging System” filed Jan. 5, 2018, now issued U.S. Pat. No. 10,352,635, which is incorporated herein by reference in its entirety. The U.S. patent application Ser. No. 15/863,856 claims the benefit of U.S. Provisional Application No. 62/443,173, filed on Jan. 6, 2017, which is incorporated herein by reference in its entirety. This application claims the benefit of U.S. Provisional Application No. 63/119,773, filed on Dec. 1, 2020, which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present invention relates to a firearm. 
     BACKGROUND 
     Referring to  FIG. 1 , a top-mounted T-shaped charging handles  2  are standard features of M-16 and AR  15  style rifles. When the charging handle  2  is pulled back towards the butstock, the operator of the firearm can eject a spent shell casing or an unfired cartridge from a chamber, load a round from the magazine, clear a jam or misfire, move a bolt into battery, and/or release a bolt locked to the rear. However, to accomplish any of these tasks, the operator of the firearm must tilt the firearm towards the ground and away from the intended target to get the leverage necessary to operate the charging handle  2 . 
     There needs to be a better way of performing these tasks without forcing the operator of the firearm to move the firearm away from the intended target. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts a top-mounted T-shaped charging handle as known in the prior art. 
         FIG. 2 a    depicts an assembled view of an upper receiver assembly according to the present disclosure. 
         FIG. 2 b    depicts a partially disassembled view of the upper receiver assembly shown in  FIG. 2   a.    
         FIG. 3  depicts another partially disassembled view of the upper receiver assembly shown in  FIG. 2   a.    
         FIG. 4  depicts a forward charging system according to the present disclosure. 
         FIGS. 5-7  depict a close up view of the forward charging system according to the present disclosure. 
         FIGS. 8-10  depict forward charging system according to the present disclosure. 
         FIGS. 11-12  depict a hand guard according to the present disclosure. 
         FIG. 13  depicts forward charging system according to the present disclosure. 
         FIGS. 14-15  depict a trap door according to the present disclosure. 
         FIGS. 16-20  depict forward charging system according to the present disclosure on a firearm using direct impingement system. 
         FIGS. 21-26  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 27  depicts an upper receiver according to some embodiments presently disclosed. 
         FIG. 28  depicts a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIGS. 29-30  depict an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 31-32  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 33  depicts an upper receiver according to some embodiments presently disclosed. 
         FIGS. 34-37  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 38  depicts a perspective view of an exemplary embodiment presently disclosed. 
         FIG. 39  depicts a perspective view of an exemplary embodiment presently disclosed. 
         FIGS. 40-41  depict an upper receiver according to some embodiments presently disclosed. 
         FIG. 42  depicts a perspective view of an exemplary embodiment presently disclosed. 
         FIGS. 43-49  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 50  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIG. 51  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 52-53  depict an exploded view of an exemplary embodiment presently disclosed. 
         FIG. 54  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIG. 55  depicts an upper receiver according to some embodiments presently disclosed. 
         FIGS. 56-58  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIGS. 59-60  depict a perspective view of a firearm according to some embodiments presently disclosed. 
         FIGS. 61-64  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 65  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 66-67  depict an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 68-69  depict a perspective view of a firearm according to some embodiments presently disclosed. 
         FIG. 70  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 71-72  depict an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 73-82  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 83  depicts a partial view of a firearm according to some embodiments presently disclosed. 
         FIGS. 84-90  depict a partially disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 91  depicts an exploded view of a firearm according to some embodiments presently disclosed. 
         FIGS. 92-95  depict a partial view of a firearm according to some embodiments presently disclosed. 
         FIGS. 96-99  depict a partial, disassembled view of a firearm according to some embodiments presently disclosed. 
         FIG. 100  depicts a partial view of a firearm according to some embodiments presently disclosed. 
         FIG. 101  depicts a partial view of a firearm according to some embodiments presently disclosed. 
         FIG. 102  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIG. 103  depicts an assembled view of an exemplary embodiment presently disclosed. 
         FIG. 104  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 105-108  depict a partial view of a firearm according to some embodiments presently disclosed. 
         FIG. 109  depicts a front view of a handguard according to some embodiments presently disclosed. 
         FIG. 110  depicts a partial view of a firearm according to some embodiments presently disclosed. 
         FIG. 111  depicts an exploded view of an exemplary embodiment presently disclosed. 
         FIGS. 112-113  depict a partial view of a firearm according to some embodiments presently disclosed. 
         FIG. 114  depicts a cutaway view of an exemplary embodiment presently disclosed. 
         FIG. 115  depicts an assembled view of an exemplary embodiment presently disclosed. 
         FIG. 116  depicts an exploded view of an exemplary embodiment presently disclosed. 
     
    
    
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of every implementation nor relative dimensions of the depicted elements, and are not drawn to scale. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to clearly describe various specific embodiments disclosed herein. One skilled in the art, however, will understand that the presently claimed invention may be practiced without all of the specific details discussed below. In other instances, well known features have not been described so as not to obscure the invention. 
     Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
     Referring to  FIG. 2 a   , an upper receiver assembly  10  is shown according to some embodiments presently disclosed. The upper receiver assembly  10  comprises a barrel  15 , a hand guard  20  and an upper receiver  25 . According to some embodiments the upper receiver  25  is coupled to a lower receiver  26  shown in  FIGS. 8-10 . The hand guard  20  may removably encircle the barrel  15 . According to some embodiments the upper receiver  25  is coupled with the barrel  15  as shown in  FIG. 2 b   . According to some embodiments the upper receiver  25  is coupled with the hand guard  20 . According to some embodiments the hand guard  20  is coupled with the barrel  15  as shown in  FIGS. 9-10 . 
     Referring to  FIGS. 2 b   - 4 , the upper receiver assembly  10  comprises a forward charging system  30  according to some embodiments presently disclosed. The forward charging system  30  comprises a charging base  40 , a charging trolley  45 , and a rod  55 . The forward charging system  30  may also comprise a return spring  50 . 
     The charging trolley  45  comprises a forward portion  60  and a rear portion  65 . According to some embodiments presently disclosed, the charging base  40  is coupled with the charging trolley  45 &#39;s forward portion  60 . According to some embodiments presently disclosed, the charging base  40  is coupled with the charging trolley  45  adjacent to the forward portion  60 . According to some embodiments presently disclosed, the charging trolley  45  comprises an opening  75  (shown in  FIG. 4 ) configured to accommodate the charging base  40  as shown in  FIG. 5 . The opening  75  may be a through opening to allow the charging base  40  to be inserted on either the right or left side of the charging trolley  45 . The charging base  40  may be coupled with the charging trolley  45  using, for example, a fastener  70  shown in  FIGS. 6-7 . The fastener  70  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. According to some embodiments presently disclosed, the charging trolley  45  comprises an opening  80  (shown in  FIGS. 5-7 ) and the charging base  40  comprises an opening  85  (shown in  FIG. 4 ). The openings  80  and  85  are configured to accommodate the fastener  70 . A set screw may be fully threaded and does not have any head projecting out of the screw thread. According to some embodiments presently disclosed, the charging base  40  is coupled substantially perpendicular to the charging trolley  45 . According to some embodiments presently disclosed, the charging base  40  is coupled at an angle to the charging trolley  45 . 
     The rod  55  comprises a forward portion  56  and a rear portion  58 . According to some embodiments presently disclosed, rod  55 &#39;s forward portion  56  is coupled with the charging trolley  45 &#39;s rear portion  65 . The rod  55  may be coupled with the charging trolley  45  using, for example, a fastener  90  shown in  FIG. 4 . The fastener  90  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. According to some embodiments presently disclosed, the charging trolley  45  comprises an opening  95  configured to accommodate rod  55 &#39;s forward portion  56 . According to some embodiments presently disclosed, the charging trolley  45  comprises an opening  100  and the rod  55  comprises an opening  105 . The openings  100  and  105  are configured to accommodate the fastener  90 . 
     According to some embodiments presently disclosed, the upper receiver  25  comprises a bolt carrier assembly  110 . The bolt carrier assembly  110  is movable between a first (locked) position and a second (unlocked) position. The bolt carrier assembly  110  supports and positions a bolt (not shown). The first (locked) position is position in which the bolt carrier  110  has positioned the bolt (not shown) for firing ammunition through the barrel  15 . The second (unlocked) position is any position other than the first (locked) position as shown in  FIGS. 8-10 . 
     According to some embodiments presently disclosed, the upper receiver  25  comprises a carrier key  115  coupled with a top portion of the bolt carrier assembly  110 . One or more fasteners  120  may be used to couple the carrier key  115  with the bolt carrier assembly  110 . The one or more fasteners  120  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. 
     According to some embodiments presently disclosed, the forward charging system  30  is configured to move the bolt carrier assembly  110  from the first (locked) position to the second (unlocked). 
     According to some embodiments presently disclosed, the charging base  40  is positioned to protrude though an opening  116  of the hand guard  20  (as shown in  FIGS. 1 and 11 ). According to some embodiments presently disclosed, the charging base  40  is positioned adjacent to the barrel  15  as shown in  FIGS. 2-3 . According to some embodiments presently disclosed, the charging base  40  is positioned away from the upper receiver  25  as shown in  FIGS. 2-3 . According to some embodiments presently disclosed, the charging base  40  is positioned away from the upper receiver  25  and towards the front of the firearm and as shown in  FIGS. 2-3 . 
     According to some embodiments presently disclosed, the hand guard  20  comprises an opening  124  configured to accommodate the barrel  15  (shown in  FIGS. 2 a    and  11 ). According to some embodiments presently disclosed, the hand guard  20  comprises one or more rails  125  extending into the opening  124 . According to some embodiments presently disclosed, the one or more rails  125  are formed during manufacturing of the hand guard  20 . According to some embodiments presently disclosed, the one or more rails  125  are extruded during manufacturing of the hand guard  20 . According to some embodiments presently disclosed, the one or more rails  125  run along the entire length of the hand guard  20 . According to some embodiments presently disclosed, the one or more rails  125  run along a portion of the hand guard  20 . 
     According to some embodiments presently disclosed, the charging trolley  45  comprises one or more channels  130  (shown in  FIGS. 5 and 12 ) configured to accommodate the one or more rails  125  as shown in  FIG. 12 . According to some embodiments presently disclosed, the one or more channels  130  run along the entire length of the charging trolley  45  as shown in  FIG. 5 . The charging trolley  45  is configured to slide along the one or more rails  125  from a first (rest) position to a second (charging) position and back to the first (rest) position. 
     According to some embodiments presently disclosed, moving the charging trolley  45  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to abut (i.e. engage) the carrier key  115 . According to some embodiments presently disclosed, moving the charging trolley  45  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to engage the carrier key  115  and move the bolt carrier assembly  110  from the first (locked) position to the second (unlocked) position. According to some embodiments presently disclosed, moving the charging trolley  45  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to move the bolt carrier assembly  110  from the first (locked) position to the second (unlocked) position. According to some embodiments presently disclosed, moving the charging trolley  45  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to engage the carrier key  115  and move the bolt carrier assembly  110  away from the barrel  15 . 
     According to some embodiments presently disclosed, the charging trolley  45 &#39;s second (charging) position is position in which the charging trolley  45  is positioned closer to the upper receiver  25 . According to some embodiments presently disclosed, the charging trolley  45 &#39;s first (rest) position is position in which the charging trolley  45  is positioned closer to the front of the firearm and away from the upper receiver  25 . According to some embodiments presently disclosed, the charging trolley  45 &#39;s second (charging) position is position in which the rod  55  moves the bolt carrier assembly  110  to the second (unlocked) position. According to some embodiments presently disclosed, the charging trolley  45 &#39;s first (rest) position is position in which the rod  55  allows the bolt carrier assembly  110  to return to the first (locked) position. According to some embodiments presently disclosed, the charging trolley  45 &#39;s first (rest) position is position in which the rod  55  is positioned away from the carrier key  115 . 
     According to some embodiments presently disclosed, the lower receiver  26  comprises a bolt hold open  145  shown in  FIG. 8 . The bolt hold open  145  is configured to move from a first (open) position to a second (blocking) position. According to some embodiments presently disclosed, at least a portion of the bolt hold open  145  moves vertically from the first (open) position to the second (blocking) position. When the bolt hold open  145  is in the first (open) position (as shown in  FIG. 10 ), the bolt carrier assembly  110  is able to freely move between the first (locking) position and the second (unlocked) position. When the bolt hold open  145  is in the second (blocking) position (as shown in  FIG. 8 ), the bolt carrier assembly  110  is prevented from moving forward to the first (locking) position. 
     According to some embodiments presently disclosed, moving the charging trolley  45  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to engage the carrier key  115  and move the bolt carrier assembly  110  away from the bolt hold open  145  thereby allowing the bolt hold open  145  to move to the first (open) position. Allowing the bolt hold open  145  to move to the first (open) position allows the bolt carrier assembly  110  to move towards the first (locked) position when the charging trolley  45  is moved towards the first (rest) position. 
     According to some embodiments presently disclosed, rod  55 &#39;s rear portion  58  is a first distance from the carrier key  115  when the charging trolley  45  is in the first (rest) position and the bolt carrier assembly  110  is in the first (locked) position. According to some embodiments presently disclosed, the first distance is about 0.05 inches. According to some embodiments presently disclosed, rod  55 &#39;s rear portion  58  is spaced away from the carrier key  115  when the charging trolley  45  is in the first (rest) position and the bolt carrier assembly  110  is in the first (locked) position. 
     According to some embodiments presently disclosed, the charging trolley  45  is moved towards the second (charging) position by applying a first force on the charging base  40  towards the second (charging) position. According to some embodiments presently disclosed, the charging trolley  45  is moved towards the second (charging) position by applying a first force on the charging base  40  towards a butstock  160  located at the rear of the firearm (shown in  FIG. 8 ). 
     According to some embodiments presently disclosed, the upper receiver  25  comprises a through opening  150  to allow the rod  55  to pass though and be able to engage the carrier key  115 . 
     According to some embodiments presently disclosed, the rod  55  passes through the return spring  50  that is positioned between the upper receiver  25  and the charging trolley  45  as shown in  FIGS. 2 b    and  13 . According to some embodiments presently disclosed, moving the charging trolley  45  towards the second (charging) position compresses the return spring  50  between the charging trolley  45  and the upper receiver  25 . According to some embodiments presently disclosed, applying the first force to the charging base  40  compresses the return spring  50  between the charging trolley  45  and the upper receiver  25 . Removing the first force causes the compressed return spring  50  to return the charging trolley  45  back to the first (rest) position. According to some embodiments presently disclosed, the return spring  50  prevents the charging trolley  45  from moving from the first (rest) position towards the second (charging position). According to some embodiments presently disclosed, the return spring  50  prevents the charging trolley  45  from moving from the first (rest) position towards the second (charging position) during normal operations of the firearm. 
     Although the charging base  40  can be used to move the charging trolley  45  from the first (rest) position towards the second (charging) position, the forward charging system  30  may further comprise a charging handle  35  coupled with the charging base  40 . The charging handle  35  may be pivotally coupled with the charging base  40 . According to some embodiments presently disclosed, the charging trolley  45  is moved towards the second (charging) position by applying a second force on the charging handle  35  towards the second (charging) position. According to some embodiments presently disclosed, the charging trolley  45  is moved towards the second (charging) position by applying a second force on the charging handle  35  towards the butstock  160  located at the rear of the firearm (shown in  FIG. 8 ). 
     According to some embodiments presently disclosed, the charging handle  35  comprises a channel (i.e. an opening)  180  configured to accommodate at least a portion of the charging base  40  (as shown in  FIG. 5 ). According to some embodiments presently disclosed, the charging handle  35  comprises a U-shaped channel  180  comprising a first sidewall  182 , a second sidewall  184  and a top wall  186  connecting the sidewalls  182  and  184 . The U-shaped channel  180  is configured to accommodate at least a portion of the charging base  40  (as shown in  FIG. 5 ). 
     According to some embodiments presently disclosed, the charging handle  35  is coupled with the charging base  40  using, for example, a fastener  165  shown in  FIG. 4 . The fastener  165  may be a pin, a spring pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. According to some embodiments presently disclosed, the charging base  40  comprises an opening  170  and the first sidewall  182  comprises an opening  175 . The openings  170  and  175  are configured to accommodate the fastener  165 . According to some embodiments presently disclosed, the second sidewall  184  also comprises an opening (not shown) configured to accommodate the fastener  165 . 
     According to some embodiments presently disclosed, the charging handle  35  is configured to pivot about the fastener  165 . According to some embodiments presently disclosed, the charging handle  35  is configured to pivot about the fastener  165  from a first (folded) position to a second (extended) position and back to the first (folded) position. According to some embodiments presently disclosed, the first (folded) position is position in which the charging handle  35  is substantially parallel to the barrel  15  (shown in  FIG. 2 a - b   ,  3  and  5 ). According to some embodiments presently disclosed, the second (extended) position is any position other than the first (folded) position as shown in  FIG. 7 . According to some embodiments presently disclosed, the second (extended) position is position in which the charging handle  35  is substantially perpendicular to the charging base  40  as shown in  FIG. 7 . 
     According to some embodiments presently disclosed, the charging base  40  comprises a forward edge  215 , a rear edge  220 , a side edge  222 , a semi circular edge  205  between the forward edge  215  and the side edge  222 , and a first cavity  210  disposed on the forward edge  215 . According to some embodiments presently disclosed, the charging base  40  may comprise a second cavity  212  disposed on the side edge  222 . 
     According to some embodiments presently disclosed, the top wall  186  of the U-shaped channel  180  comprises an opening  190  configured to accommodate a spring  195  and a ball bearing  200  as shown in  FIGS. 4, 6-7 . According to some embodiments presently disclosed, the spring  195  is disposed in the opening  190  and the ball bearing  200  is disposed between the spring  195  and the charging base  40 . When the charging handle  35  is in the first (folded) position, the ball bearing  200  is positioned in the first cavity  210  to prevent the charging handle  35  from moving to the second (extended) position. According to some embodiments presently disclosed, after applying a third force to the charging handle  35 , the ball bearing  200  is pushed out of the first cavity  210  and rolls along the semi-circular edge  205  until the top wall  186  abuts the side edge  222  and/or until the charging handle  35  reaches the second (extended) position. According to some embodiments presently disclosed, after applying a third force to the charging handle  35 , the ball bearing  200  is pushed out of the cavity  210  and rolls along the semi-circular edge  205  until it is positioned in the second cavity  212 . According to some embodiments presently disclosed, when the charging handle  35  is in the second (extended) position, the ball bearing  200  is positioned in the second cavity  212  to prevent the charging handle  35  from moving to the first (folded) position. According to some embodiments presently disclosed, a force of the spring  50  returning the charging trolley  45  back to the first (rest) position causes the charging handle  35  to move from the second (extended) position to the first (folded) position. According to some embodiments presently disclosed, a force of the spring  50  returning the charging trolley  45  back to the first (rest) position causes the charging handle  35  to move from the second (extended) position to the first (folded) position and position the ball bearing  200  in the cavity  210 . According to some embodiments presently disclosed, a force of the spring  50  returning the charging trolley  45  back to the first (rest) position causes the ball bearing  200  to be pushed out of the cavity  212  and roll in to the cavity  210 . 
     According to some embodiments presently disclosed, the upper receiver  25  comprises a trap door  230  (shown in  FIGS. 14-15 ). The trap door  230  may be pivotally coupled with the upper receiver  25 . The rap door  230  is pivotally movable from the first (open) position (shown in  FIG. 14 ) to the second (closed) position (shown in  FIG. 15 ) and back to the first (open) position. The trap door  230  may be moved to the first (open) position when the upper receiver  25  is at least partially removed (i.e. pivoted away) from the lower receiver  26 . The carrier key  115  coupled with the bolt carrier assembly  110  may be removed from the upper receiver  25  when the trap door  230  is in the first (open) position as shown in  FIG. 14 . The trap door  230  is securely locked in the second (closed) position when the upper receiver  25  is coupled with the lower receiver  26  as shown in  FIG. 15 . The lower receiver  26  prevents the trap door  230  from moving towards the first (open) position when the upper receiver  25  is coupled with the lower receiver  26  as shown in  FIG. 15 . 
     It is to be understood that the forward charging system  30  described above may be implemented on different types of firearms. The forward charging system  30  described above may be implemented on firearms using a blowback system of operation, and/or firearm using a direct impingement system of operation, and/or firearm using piston system of operation. Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas crated by the ignition of the propellant charge. Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly into the bolt carrier to cycle the action. Piston system uses gas pressure to mechanically move the bolt carrier to cycle the action. It is also to be understood that the forward charging system  30  described above may be implemented on M-16 and Armalite style rifles (ARs). 
     Referring to  FIGS. 16-20 , the forward charging system  30  is shown on an upper receiver assembly  300  using for example, a direct impingement system. Referring to  FIGS. 16-17 , the upper receiver assembly  300  is shown according to some embodiments presently disclosed. The upper receiver assembly  300  comprises a barrel  325 , gas block  310  coupled with the barrel, gas tube  315 , and an upper receiver  320 . The upper receiver assembly  300  may comprise a hand guard  20  as shown in  FIG. 11  and described above. According to some embodiments presently disclosed, the upper receiver assembly  300  comprises the forward charging system  30  as described above. 
     Referring to  FIGS. 16-17 , the charging trolley  45  may be positioned above the gas block  310 . The rod  55  may be positioned above the gas tube  315 . Referring to  FIGS. 18-19 , the upper receiver  320  comprises an opening  330  (shown in  FIG. 18 ) to accommodate the rod  55  (shown in  FIG. 19 ) and an opening  335  (shown in  FIG. 18 ) to accommodate the gas tube  315  (shown in  FIG. 19 ). 
     According to some embodiments presently disclosed, the upper receiver  320  comprises a bolt carrier assembly  340 . The bolt carrier assembly  340  is movable between a first (i.e. locked) position and a second (i.e. unlocked) position. The bolt carrier assembly  340  supports and positions a bolt (not shown). The first (locked) position is position in which the bolt carrier  340  has positioned the bolt (not shown) for firing ammunition through the barrel  325 . The second (unlocked) position is any position other than the first (locked) position. 
     According to some embodiments presently disclosed, the upper receiver  320  comprises a carrier key  345  coupled with a top portion of the bolt carrier assembly  340 . One or more fasteners  350  may be used to couple the carrier key  345  with the bolt carrier assembly  340 . The one or more fasteners  350  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. The carrier key  345  comprises a surface  360  configured to abut the rod  55  when the bolt carrier  340  is being moved from away from the first (locked) position. The surface  360  comprises an opening  365  configured to accommodate the gas tube  315 . 
     According to some embodiments presently disclosed, the forward charging system  30  as described in detail above is configured to move the bolt carrier assembly  340  from the first (locked) position to the second (unlocked) position. 
     According to some embodiments presently disclosed, the hand guard  20  (shown in  FIG. 11 ) may comprise opening  116  on either right side of the firearm or left side of the firearm or on both sides of the firearm. This allows the operator of the firearm to position the charging base  40  on either side of the firearm depending if the operator is right handed or left handed. 
     According to some embodiments presently disclosed, the hand guard  20  (shown in  FIG. 11 ) may comprise multiple openings  116  along the hand guard  20 . Having multiple opening  116  available along the hand guard  20  allow the operator to select how far the charging base  40  is from the upper receiver  25 . If the operator of the firearm has long arms, the charging base  40  may be placed through an opening  116  located farther away from the upper receiver  25 . If the operator of the firearm has short arms, the charging base  40  may be placed through an opening  116  located closer to the upper receiver  25 . According to some embodiments presently disclosed, the forward charging system  30  may be provided with different length rods  55  to accommodate operators with different arm lengths. According to some embodiments presently disclosed, the forward charging system  30  may be provided with the rod  55  having adjustable length to accommodate operators with different arm lengths. According to some embodiments presently disclosed, the forward charging system  30  may be provided with the rod  55  that can be shortened to accommodate operators with shorter arm. 
     Referring to  FIGS. 21-26 , a portion of a firearm  500  is shown according to some embodiments presently disclosed. The firearm  500  may comprise a barrel  515 , a hand guard  520  and an upper receiver  525  (shown in  FIG. 27 ). According to some embodiments, the upper receiver  525  may be removably coupled to a lower receiver  526 . According to some embodiments, the hand guard  520  may removably encircle the barrel  515 . According to some embodiments the upper receiver  525  may be removably coupled with the barrel  515 . According to some embodiments the upper receiver  525  may be removably coupled with the hand guard  520 . According to some embodiments the hand guard  520  may be removably coupled with the barrel  515  as shown in  FIGS. 23-24 . According to some embodiments presently disclosed, the firearm  500  comprises, for example, a direct impingement system. Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly into the bolt carrier to cycle the action. The firearm  500  comprises a gas block  511  coupled with the barrel  515 , and a gas tube  512  ( FIG. 23 ). 
     Referring to  FIGS. 23-26 , the firearm  500  comprises the forward charging system  30  according to some embodiments presently disclosed. According to some embodiments presently disclosed, the firearm  500  comprises the forward charging system  30  as described above. 
     Referring to  FIGS. 23-26 , the charging trolley  45  may be positioned above the gas block  511 . The rod  55  may be positioned above the gas tube  512 . Referring to  FIGS. 27-28 , the upper receiver  525  comprises an opening  530  (shown in  FIG. 27 ) to accommodate the rod  55  (shown in  FIG. 28 ) and an opening  535  (shown in  FIG. 27 ) to accommodate the gas tube  512  (shown in  FIG. 28 ). 
     According to some embodiments presently disclosed, the firearm  500  comprises a bolt carrier assembly  540  ( FIGS. 23 and 50 ). According to some embodiments presently disclosed, the bolt carrier assembly  540  is movable between a first (i.e. locked) position (shown in  FIGS. 21, 24, 73 and 75 ) and a second (i.e. unlocked) position (shown in  FIGS. 22, 23, 74 and 76 ). According to some embodiments presently disclosed, the bolt carrier assembly  540  is movable between a first (i.e. locked) position (shown in  FIGS. 21, 24, 73 and 75 ) and a second (i.e. unlocked) position (shown in  FIGS. 22, 23, 74 and 76 ) by the forward charging system  30 . 
     The bolt carrier assembly  540  comprises a bolt carrier  701 , a bolt assembly  702 , a cam pin  703 , a firing pin  704 , a firing pin retaining pin  705 , a carrier key  545  ( FIG. 50 ). The bolt carrier assembly  540  supports and positions the bolt assembly  702 . Referring to  FIGS. 21, 24, 73 and 75 , according to some embodiments, the first (locked) position is position in which the bolt carrier assembly  540  has positioned the bolt assembly  702  for firing ammunition through the barrel  515 . Referring to  FIGS. 21, 24, 73 and 75 , according to some embodiments, the first (locked) position is position in which the bolt carrier assembly  540  locks the bolt assembly  702  into battery. Referring to  FIGS. 21, 24, 73 and 75 , according to some embodiments, the first (locked) position is position in which the bolt carrier assembly  540  is locked into battery. Referring to  FIGS. 22, 23, 74 and 76 , according to some embodiments, the second (unlocked) position is any position other than the first (locked) position. 
     According to some embodiments presently disclosed, the forward charging system  30  as described in detail above is configured to move the bolt carrier assembly  540  from the first (locked) position to the second (unlocked) position. 
     Referring to  FIGS. 29-30 and 50 , according to some embodiments presently disclosed, the carrier key  545  is removably coupled with a top portion of the bolt carrier  701 . One or more fasteners  550  may be used to couple the carrier key  545  with the bolt carrier assembly  540 . The one or more fasteners  550  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. 
     According to some embodiments presently disclosed, the carrier key  545  comprises a surface  560  configured to abut the rod  55  when the bolt carrier assembly  540  is being moved away from the first (locked) position. According to some embodiments presently disclosed, the surface  560  comprises an aperture (i.e. opening)  565  configured to accommodate the gas tube  512 . According to some embodiments presently disclosed, the surface  560  may also comprise a through aperture  566  configured to accommodate a recoil spring guide rod  567  described in more detail below. According to some embodiments, the through aperture  566  is a through-opening. According to some embodiments, the diameter of the rod  55  is larger than the diameter of the aperture  566 . Referring to  FIGS. 29-30 and 51 , according to some embodiments presently disclosed, the firearm  500  comprises the recoil spring guide rod  567 , recoil spring  568 , and a plug  569 . 
     According to some embodiments presently disclosed, the rod  55  comprises an aperture  573  ( FIG. 29 ). According to some embodiments presently disclosed, the rod  55  is a hollow tube that defines the aperture  573 . According to some embodiments presently disclosed, the aperture  573  goes through a portion of the rod  55 . According to some embodiments presently disclosed, the aperture  573  goes through an entire length of the rod  55 . 
     The recoil spring guide rod  567  comprises a forward portion  571  and a rear portion  572 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  is configured to go through the aperture  566  and into the aperture  573 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  is configured to abut the plug  569 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  545  and the plug  566 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  has a diameter that is larger than the diameter of the rest of the recoil spring guide rod  567 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  545  and larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . 
     According to some embodiments, the bolt carrier assembly  540  is configured to slide along the recoil spring guide rod  567  between the first (i.e. locked) position and a second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  always resides in the aperture  573 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  resides in the aperture  573  when the bolt carrier assembly  540  is in the first (i.e. locked) position and when the bolt carrier assembly  540  is in the second (i.e. unlocked) position ( FIGS. 25-26 ). According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  resides in the aperture  573  when the bolt carrier assembly  540  is in the second (i.e. unlocked) position ( FIGS. 31-32 ). According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across the entire lengths of the upper receiver  525 . According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across the entire lengths of the lower receiver  526 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  extends into the aperture  530  through the aperture  573  ( FIGS. 25-26 ). 
     According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across a portion of the upper receiver  525  ( FIGS. 31-32 ). According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across a portion of the lower receiver  526  ( FIGS. 31-32 ). 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  resides in the aperture  573  only when the charging trolley  45  is in the second (charging) position. 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the upper receiver  525 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the lower receiver  526 . 
     According to some embodiments, the bolt carrier assembly  540  does not extend beyond the lower receiver  526  when in the second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, moving the bolt carrier assembly  540  towards the second (unlocked) position compresses the recoil spring  568  between the bolt carrier assembly  540  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  540  compresses the recoil spring  568  between the bolt carrier assembly  540  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  540  compresses the recoil spring  568  between the bolt carrier assembly  540  and the larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . Removing the first force causes the compressed recoil spring  568  to move the bolt carrier assembly  540  towards the first (locked) position. 
     According to some embodiments presently disclosed, the upper receiver  525  comprises an aperture  575  ( FIG. 33 ) configured to accommodate the bolt carrier assembly  540 , the recoil spring  568 , and the recoil spring guide rod  567 . According to some embodiments presently disclosed, the plug  569  abuts the upper receiver  525  to prevent the bolt carrier assembly  540 , the recoil spring  568 , and the recoil spring guide rod  567  from being removed from the upper receiver  525 . 
     Referring to  FIGS. 34-37 and 73-76 , according to some embodiments presently disclosed, the lower receiver  526  comprises openings for accepting the internal mechanisms required to operate the firearm. For example, the lower receiver  526  may comprise an opening  581  configured to accept an ammunition magazine (not shown) and associated hardware to direct rounds loaded within the magazine into a chamber in an upper receiver  525 . The lower receiver  526  may also comprise an opening  582  configured to accommodate a firing mechanism (i.e. standard trigger group). According to some embodiments, the firing mechanism (i.e. standard trigger group) comprises a trigger mechanism  583  and a hammer mechanism  584 . 
     Referring to  FIGS. 34-37 and 73-76 , according to some embodiments presently disclosed, the lower receiver  526  comprises a bolt hold open  585 , an opening  586  configured to accommodate the bolt hold open  585 . Referring to  FIGS. 73-76 , according to some embodiments presently disclosed, the opening  582  is separated from the opening  586  by a wall  2500 . 
     Referring to  FIGS. 36-37 , according to some embodiments presently disclosed, the lower receiver  526  comprises an upwardly extending lobe  587 . According to some embodiments, the upwardly extending lobe  587  is integrally coupled with the lower receiver  526 . According to some embodiments, the upwardly extending lobe  587  extends from the lower receiver  526 . 
     According to some embodiments, the upwardly extending lobe  587  is used to mount a buttstock (not shown) to the lower receiver  526 . According to some embodiments, the upwardly extending lobe  587  comprises a generally circular threaded through-hole  589 . According to some embodiments presently disclosed, the upwardly extending lobe  587  is configured to accommodate a portion of the bolt carrier assembly  540  when the bolt carrier assembly  540  is in the second (unlocked) position. According to some embodiments presently disclosed, the generally circular threaded through-hole  589  is configured to accommodate a portion of the bolt carrier assembly  540  when the bolt carrier assembly  540  is in the second (unlocked) position. 
     Referring to  FIGS. 36-39 , according to some embodiments presently disclosed, the firearm  500  comprises a first end plate  591  and a second end plate  592 . 
     According to some embodiments presently disclosed, the first end plate  591  comprises a first surface  593  and a second surface  594  positioned opposite the first surface  593 . According to some embodiments presently disclosed, the first end plate  591  comprises an outer threaded surface  595  adapted to mate with the generally circular threaded through-hole  589 . According to some embodiments, the generally circular threaded through-hole  589  is adapted to receive the mating male threads  595  on the first end plate  591 . According to some embodiments presently disclosed, the first end plate  591  is configured to be threaded into the generally circular threaded through-hole  589 . According to some embodiments presently disclosed, the first end plate  591  is configured to be threaded into the generally circular threaded through-hole  589  from the side closest to the opening  582 . 
     According to some embodiments presently disclosed, the first end plate  591  prevents the bolt carrier assembly  540  from being positioned beyond the lower receiver  526  when the bolt carrier assembly is in the second (unlocked) position. 
     According to some embodiments presently disclosed, the first end plate  591  comprises a protrusion  596  extending from the second surface  594 . According to some embodiments presently disclosed, the protrusion  596  comprises an outer threaded surface  597 . 
     According to some embodiments presently disclosed, the second end plate  592  comprises a first surface  598  and a second surface  599  positioned opposite the first surface  598 . According to some embodiments presently disclosed, the first surface  598  of the second end plate  592  comprises a threaded aperture  601 . 
     According to some embodiments presently disclosed, the threaded aperture  601  is adapted to mate with the protrusion  596 . According to some embodiments, the threaded aperture  601  is adapted to receive the mating male threads  597  on the protrusion  596 . According to some embodiments presently disclosed, the first end plate  591  is configured to be threaded into the second end plate  592 . According to some embodiments presently disclosed, the second end plate  592  is coupled with the upwardly extending lobe  587  with the first end plate  591 . According to some embodiments presently disclosed, the second end plate  592  is coupled to the upwardly extending lobe  587  from the side that is farthest from the opening  582 . 
     According to some embodiments presently disclosed, the second surface  599  comprises one or more rails  602  configured to accommodate one or more accessories. According to some embodiments presently disclosed, the second surface  599  comprises one or more rails  602  to allow coupling of one or more accessories to the lower receiver  526 . 
     Referring to  FIGS. 29-30 , according to some embodiments presently disclosed, the firearm  500  comprises a recoil buffer  603 . The recoil buffer  603  may be positioned to abut the first surface  593  of the first end plate  591 . According to some embodiments presently disclosed, the recoil buffer  603  may be used to prevent prevents the bolt carrier assembly  540  from being slammed into the first end plate  591  when the bolt carrier assembly  540  is in the second (unlocked) position. 
     Referring to  FIGS. 40-42 , according to some embodiments presently disclosed, the plug  569  is removably coupled with the upper receiver  525 . The plug  569  compromises a first side  607  and a protrusion  608  extending from the first side  607 . The protrusion  608  may comprise a wider portion  609  extending outwardly from the protrusion  608 . 
     According to some embodiments presently disclosed, the upper receiver  525  comprises a channel  610  configured to accommodate the wider portion  609  of the plug  569 . 
     According to some embodiments presently disclosed, the protrusion  608  comprises an indentation  613  configured to accommodate the larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . According to some embodiments presently disclosed, the protrusion  608  comprises an aperture  613  configured to accommodate the larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . 
     Referring to  FIGS. 43-49 , a portion of a firearm  800  is shown according to some embodiments presently disclosed. The firearm  800  may comprise a barrel  815 , a hand guard  820  and an upper receiver  825  (shown in  FIG. 49 ). According to some embodiments, the upper receiver  825  may be coupled to a lower receiver  826 . According to some embodiments, the hand guard  820  may removably encircle the barrel  815 . According to some embodiments the upper receiver  825  may be removably coupled with the barrel  815 . According to some embodiments the upper receiver  825  may be removably coupled with the hand guard  820 . According to some embodiments the hand guard  820  may be removably coupled with the barrel  815  as shown in  FIGS. 46-48 . 
     According to some embodiments presently disclosed, the firearm  800  uses a blowback system of operation. Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas crated by the ignition of the propellant charge. 
     Referring to  FIGS. 46-48 , the firearm  800  comprises the forward charging system  30  according to some embodiments presently disclosed. According to some embodiments presently disclosed, the firearm  800  comprises the forward charging system  30  as described above. 
     Referring to  FIG. 49 , the upper receiver  825  comprises an opening  850  to accommodate the rod  55 . 
     According to some embodiments presently disclosed, the firearm  800  comprises a bolt carrier assembly  840  ( FIGS. 52-54 ). According to some embodiments presently disclosed, the bolt carrier assembly  840  is movable between a first (i.e. locked) position (shown in  FIGS. 43, 46 and 77 ) and a second (i.e. unlocked) position (shown in  FIGS. 44-45, 47-48 and 78 ). According to some embodiments presently disclosed, the bolt carrier assembly  840  is movable between a first (i.e. locked) position (shown in  FIGS. 43, 46 and 77 ) and a second (i.e. unlocked) position (shown in  FIGS. 44-45, 47-48 and 78 ) by the forward charging system  30 . 
     The bolt carrier assembly  840  comprises a bolt carrier  901 , an extractor  902 , a cam pin  703 , a firing pin  904 , a carrier key  845  ( FIG. 55 ). The bolt carrier assembly  840  supports and positions the bolt carrier  901 . Referring to  FIGS. 43 and 46 , the first (locked) position is position in which the bolt carrier assembly  840  has positioned the bolt carrier  901  for firing ammunition through the barrel  815 . Referring to  FIGS. 43, 46 and 77 , according to some embodiments, the first (locked) position is position in which the bolt carrier assembly  840  is locked into battery. Referring to  FIGS. 44-45, 47-48 and 78 , the second (unlocked) position is any position other than the first (locked) position. 
     According to some embodiments presently disclosed, the forward charging system  30  as described in detail above is configured to move the bolt carrier assembly  840  from the first (locked) position to the second (unlocked) position. 
     Referring to  FIG. 54 , according to some embodiments presently disclosed, the carrier key  845  is removably coupled with a top portion of the bolt carrier  901 . One or more fasteners  850  may be used to couple the carrier key  845  with the bolt carrier assembly  840 . The one or more fasteners  850  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. 
     According to some embodiments presently disclosed, the carrier key  845  comprises a surface  860  configured to abut the rod  55  when the bolt carrier assembly  840  is being moved away from the first (locked) position. According to some embodiments presently disclosed, the surface  860  comprises a through aperture  866  configured to accommodate a recoil spring guide rod  567  described in more detail below. According to some embodiments, the through aperture  866  is a through-opening. According to some embodiments, the diameter of the rod  55  is larger than the diameter of the aperture  866 . 
     Referring to  FIGS. 51-53 , according to some embodiments presently disclosed, the firearm  800  comprises the recoil spring guide rod  567 , the recoil spring  568 , and the plug  569  as described in detail above and below. 
     According to some embodiments presently disclosed, the firearm  800  comprises the rod  55  wherein the rod  55  comprises an aperture  573  ( FIG. 52 ). According to some embodiments presently disclosed, the rod  55  is a hollow tube that defines the aperture  573 . According to some embodiments presently disclosed, the aperture  573  goes through a portion of the rod  55 . According to some embodiments presently disclosed, the aperture  573  goes through an entire length of the rod  55 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  is configured to go through the aperture  566  and into the aperture  573 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  is configured to abut the plug  569 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  545  and the plug  566 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  has a diameter that is larger than the diameter of the rest of the recoil spring guide rod  567 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  545  and larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . 
     According to some embodiments, the bolt carrier assembly  840  is configured to slide along the recoil spring guide rod  567  between the first (i.e. locked) position and a second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  always resides in the aperture  573 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  resides in the aperture  573  when the bolt carrier assembly  840  is in the first (i.e. locked) position and when the bolt carrier assembly  840  is in the second (i.e. unlocked) position ( FIGS. 43-44 ). According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  resides in the aperture  573  when the bolt carrier assembly  540  is in the second (i.e. unlocked) position ( FIG. 48 ). According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across the entire lengths of the upper receiver  825 . According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across the entire lengths of the lower receiver  826 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  extends into the aperture  850  through the aperture  573  ( FIG. 45 ). 
     According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across a portion of the upper receiver  825 . According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across a portion of the lower receiver  826 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  resides in the aperture  573  only when the charging trolley  45  is in the second (charging) position. 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the upper receiver  825 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the lower receiver  826 . 
     According to some embodiments, the bolt carrier assembly  840  does not extend beyond the lower receiver  826  when in the second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, moving the bolt carrier assembly  840  towards the second (unlocked) position compresses the recoil spring  568  between the bolt carrier assembly  840  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  840  compresses the recoil spring  568  between the bolt carrier assembly  840  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  840  compresses the recoil spring  568  between the bolt carrier assembly  840  and the larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . Removing the first force causes the compressed recoil spring  568  to move the bolt carrier assembly  840  towards the first (locked) position. 
     According to some embodiments presently disclosed, the upper receiver  825  comprises an aperture  875  ( FIG. 55 ) configured to accommodate the bolt carrier assembly  840 , the recoil spring  568 , and the recoil spring guide rod  567 . According to some embodiments presently disclosed, the plug  569  abuts the upper receiver  825  to prevent the bolt carrier assembly  840 , the recoil spring  568 , and the recoil spring guide rod  567  from being removed from the upper receiver  825 . 
     Referring to  FIGS. 56-58 and 77-78 , according to some embodiments presently disclosed, the lower receiver  826  comprises openings for accepting the internal mechanisms required to operate the firearm. For example, the lower receiver  826  may comprise an opening  881  configured to accept an ammunition magazine (not shown) and associated hardware to direct rounds loaded within the magazine into a chamber in an upper receiver  825 . The lower receiver  826  may also comprise an opening  882  configured to accommodate a firing mechanism (i.e. standard trigger group). According to some embodiments, the firing mechanism (i.e. standard trigger group) comprises a trigger mechanism  583  and a hammer mechanism  584 . 
     Referring to  FIGS. 56-58 and 77-78 , according to some embodiments presently disclosed, the lower receiver  826  comprises a bolt hold open  885 , an opening  886  configured to accommodate the bolt hold open  885 . Referring to  FIGS. 77-78 , according to some embodiments presently disclosed, the opening  882  is separated from the opening  886  by a wall  2501 . 
     Referring to  FIGS. 56-58 and 77-78 , according to some embodiments presently disclosed, the lower receiver  826  comprises an upwardly extending lobe  887 . According to some embodiments, the upwardly extending lobe  887  is integrally coupled with the lower receiver  826 . According to some embodiments, the upwardly extending lobe  887  extends from the lower receiver  826 . 
     According to some embodiments, the upwardly extending lobe  887  is used to mount a buttstock (not shown) to the lower receiver  826 . According to some embodiments, the upwardly extending lobe  887  comprises a generally circular threaded through-hole  889 . 
     According to some embodiments presently disclosed, the upwardly extending lobe  887  is configured to accommodate a portion of the bolt carrier assembly  840  when the bolt carrier assembly  840  is in the second (unlocked) position. According to some embodiments presently disclosed, the generally circular threaded through-hole  889  is configured to accommodate a portion of the bolt carrier assembly  840  when the bolt carrier assembly  840  is in the second (unlocked) position. 
     Referring to  FIGS. 38-39 and 56-57 , according to some embodiments presently disclosed, the firearm  800  comprises the first end plate  591  and the second end plate  592  as described in more detail above. 
     According to some embodiments presently disclosed, the first end plate  591  prevents the bolt carrier assembly  840  from being positioned beyond the lower receiver  826  when the bolt carrier assembly is in the second (unlocked) position. 
     According to some embodiments presently disclosed, the second end plate  592  is coupled with the upwardly extending lobe  887  with the first end plate  591 . According to some embodiments presently disclosed, the second end plate  592  is coupled to the upwardly extending lobe  887  from the side that is farthest from the opening  882 . 
     Referring to  FIGS. 52-53 , according to some embodiments presently disclosed, the firearm  800  comprises the recoil buffer  603  as described above. 
     Referring to  FIGS. 52-53 , according to some embodiments presently disclosed, the firearm  800  comprises the plug  569  removably coupled with the upper receiver  825 . 
     Referring to  FIGS. 59-60 , a firearm  1000  is shown according to some embodiments presently disclosed. The firearm  1000  may comprise a barrel  1015 , a hand guard  1020  and an upper receiver  1025 . According to some embodiments, the upper receiver  1025  may be coupled to a lower receiver  1026 . According to some embodiments, the hand guard  1020  may removably encircle the barrel  1015 . According to some embodiments the upper receiver  1025  may be removably coupled with the barrel  1015 . According to some embodiments the upper receiver  1025  may be removably coupled with the hand guard  1020 . According to some embodiments the hand guard  1020  may be removably coupled with the barrel  1015  as shown in  FIGS. 63-64 . 
     According to some embodiments presently disclosed, the firearm  1000  comprises, for example, a direct impingement system. Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly into the bolt carrier to cycle the action. The firearm  1000  comprises a gas block  1011  coupled with the barrel  1015 , and a gas tube  1012  ( FIGS. 63-64 ). 
     Referring to  FIGS. 59-64 , the firearm  1000  comprises a removable side charging handle  1001  according to some embodiments presently disclosed. According to some embodiments presently disclosed, the firearm  1000  comprises the side charging handle  1001  coupled with the bolt carrier assembly  1040  as described below. According to some embodiments presently disclosed, the side charging handle  1001  protrudes from the upper receiver  1025  ( FIGS. 59-60 ). 
     According to some embodiments, the upper receiver  1025  comprises an opening  1030  (shown in  FIG. 62 ) to accommodate the gas tube  512  and an opening  1035  (shown in  FIG. 62 ) to accommodate a recoil spring guide rod  567  described in more detail above and below (shown in  FIG. 62 ). 
     According to some embodiments presently disclosed, the firearm  1000  comprises the bolt carrier assembly  1040  ( FIG. 65 ). According to some embodiments presently disclosed, the bolt carrier assembly  1040  is movable between a first (i.e. locked) position (shown in  FIGS. 61, 63 and 79 ) and a second (i.e. unlocked) position (shown in  FIGS. 62, 64 and 80 ). According to some embodiments presently disclosed, the bolt carrier assembly  1040  is movable between a first (i.e. locked) position (shown in  FIGS. 61, 63 and 79 ) and a second (i.e. unlocked) position (shown in  FIGS. 62, 64 and 80 ) by the side charging handle  1001 . 
     The bolt carrier assembly  1040  comprises a bolt carrier  1101 , a bolt assembly  1102 , a cam pin  1103 , a firing pin  1104 , a firing pin retaining pin  1105 , a carrier key  1045  ( FIG. 65 ). The bolt carrier assembly  1040  supports and positions the bolt assembly  1102 . Referring to  FIGS. 61 and 63 , the first (locked) position is position in which the bolt carrier assembly  1040  has positioned the bolt assembly  1102  for firing ammunition through the barrel  1015 . Referring to  FIGS. 61, 63 and 79 , according to some embodiments, the first (locked) position is position in which the bolt carrier assembly  1040  locks the bolt assembly  1102  into battery. Referring to  FIGS. 61, 63 and 79 , according to some embodiments, the first (locked) position is position in which the bolt carrier assembly  1040  is locked into battery. Referring to  FIGS. 62, 64 and 80 , the second (unlocked) position is any position other than the first (locked) position. 
     According to some embodiments presently disclosed, the side charging handle  1001  is configured to move the bolt carrier assembly  1040  from the first (locked) position to the second (unlocked) position. According to some embodiments presently disclosed, the firearm  1000  also comprises the forward charging system  30  as described in detail above. According to some embodiments presently disclosed, the firearm  1000  also comprises the forward charging system  30  as described in detail above, wherein the forward charging system  30  and the side charging handle  1001  are configured to move the bolt carrier assembly  1040  from the first (locked) position to the second (unlocked) position. 
     Referring to  FIG. 65 , according to some embodiments presently disclosed, the carrier key  1045  is removably coupled with a top portion of the bolt carrier  1101 . One or more fasteners  1050  may be used to couple the carrier key  1045  with the bolt carrier assembly  1040 . The one or more fasteners  1050  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. 
     According to some embodiments presently disclosed, the carrier key  1045  comprises a surface  1060 . According to some embodiments presently disclosed, the surface  1060  comprises an aperture (i.e. opening)  1065  configured to accommodate the gas tube  1012 . According to some embodiments presently disclosed, the surface  1060  may also comprise a through aperture  1066  configured to accommodate a recoil spring guide rod  567  described in more detail below. According to some embodiments, the through aperture  1066  is a through-opening. 
     Referring to  FIGS. 66-67 , according to some embodiments presently disclosed, the firearm  1000  comprises the recoil spring guide rod  567 , the recoil spring  568 , and the plug  569  as described above and below. 
     The recoil spring guide rod  567  comprises a forward portion  571  and a rear portion  572 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  is configured to go through the aperture  1066  and into the aperture  1035 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  is configured to abut the plug  569 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  1045  and the plug  566 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  has a diameter that is larger than the diameter of the rest of the recoil spring guide rod  567 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  1045  and larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . 
     According to some embodiments, the bolt carrier assembly  1040  is configured to slide along the recoil spring guide rod  567  between the first (i.e. locked) position and a second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across the entire lengths of the upper receiver  1025 . According to some embodiments presently disclosed, the recoil spring guide rod  567  extends across the entire lengths of the lower receiver  1026 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the upper receiver  1025 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the lower receiver  1026 . 
     According to some embodiments, the bolt carrier assembly  1040  does not extend beyond the lower receiver  1026  when in the second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, moving the bolt carrier assembly  1040  towards the second (unlocked) position compresses the recoil spring  568  between the bolt carrier assembly  1040  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  1040  compresses the recoil spring  568  between the bolt carrier assembly  1040  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  1040  compresses the recoil spring  568  between the bolt carrier assembly  1040  and the larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . Removing the first force causes the compressed recoil spring  568  to move the bolt carrier assembly  1040  towards the first (locked) position. 
     According to some embodiments presently disclosed, the upper receiver  1025  comprises an aperture configured to accommodate the bolt carrier assembly  1040 , the recoil spring  568 , and the recoil spring guide rod  567 . According to some embodiments presently disclosed, the plug  569  abuts the upper receiver  1025  to prevent the bolt carrier assembly  1040 , the recoil spring  568 , and the recoil spring guide rod  567  from being removed from the upper receiver  1025 . 
     Referring to  FIGS. 63-64 and 79-80 , according to some embodiments presently disclosed, the lower receiver  1026  comprises openings for accepting the internal mechanisms required to operate the firearm. For example, the lower receiver  1026  may comprise an opening  1081  configured to accept an ammunition magazine (not shown) and associated hardware to direct rounds loaded within the magazine into a chamber in an upper receiver  1025 . The lower receiver  1026  may also comprise an opening  1082  configured to accommodate a firing mechanism (i.e. standard trigger group). According to some embodiments, the firing mechanism (i.e. standard trigger group) comprises a trigger mechanism  583  and a hammer mechanism  584 . 
     Referring to  FIGS. 63-64 and 79-80 , according to some embodiments presently disclosed, the lower receiver  1026  comprises a bolt hold open  1085 , an opening  1086  configured to accommodate the bolt hold open  1085 . Referring to  FIGS. 79-80 , according to some embodiments presently disclosed, the opening  1082  is separated from the opening  1086  by a wall  2502 . 
     Referring to  FIGS. 63-64 , according to some embodiments presently disclosed, the lower receiver  1026  comprises an upwardly extending lobe  1087 . According to some embodiments, the upwardly extending lobe  1087  is integrally coupled with the lower receiver  1026 . According to some embodiments, the upwardly extending lobe  1087  extends from the lower receiver  1026 . 
     According to some embodiments, the upwardly extending lobe  1087  is used to mount a buttstock (not shown) to the lower receiver  1026 . According to some embodiments, the upwardly extending lobe  1087  comprises a generally circular threaded through-hole. 
     According to some embodiments presently disclosed, the upwardly extending lobe  1087  is configured to accommodate a portion of the bolt carrier assembly  1040  when the bolt carrier assembly  1040  is in the second (unlocked) position. According to some embodiments presently disclosed, the generally circular threaded through-hole is configured to accommodate a portion of the bolt carrier assembly  1040  when the bolt carrier assembly  1040  is in the second (unlocked) position. 
     Referring to  FIGS. 66-67 , according to some embodiments presently disclosed, the firearm  1000  comprises the first end plate  591  and the second end plate  592  as described above. 
     According to some embodiments presently disclosed, the first end plate  591  is configured to be threaded into the generally circular threaded through-hole from the side closest to the opening  1082 . 
     According to some embodiments presently disclosed, the first end plate  591  prevents the bolt carrier assembly  1040  from being positioned beyond the lower receiver  1026  when the bolt carrier assembly is in the second (unlocked) position. 
     According to some embodiments presently disclosed, the second end plate  592  is coupled with the upwardly extending lobe  1087  with the first end plate  591 . According to some embodiments presently disclosed, the second end plate  592  is coupled to the upwardly extending lobe  1087  from the side that is farthest from the opening  1082 . 
     Referring to  FIGS. 66-67 , according to some embodiments presently disclosed, the firearm  1000  comprises the recoil buffer  603  as described above. The recoil buffer  603  may be positioned to abut the first end plate  591 . According to some embodiments presently disclosed, the recoil buffer  603  may be used to prevent prevents the bolt carrier assembly  1040  from being slammed into the first end plate  591  when the bolt carrier assembly  1040  is in the second (unlocked) position. 
     Referring to  FIGS. 66-67 , according to some embodiments presently disclosed, the plug  569  (described above) is removably coupled with the upper receiver  1025 . 
     Referring to  FIGS. 68-69 , a firearm  1200  is shown according to some embodiments presently disclosed. The firearm  1000  may comprise a barrel  1215 , a hand guard  1220  and an upper receiver  1225 . According to some embodiments, the upper receiver  1025  may be coupled to a lower receiver  1226 . According to some embodiments, the hand guard  1220  may removably encircle the barrel  1215 . According to some embodiments the upper receiver  1025  may be removably coupled with the barrel  1215 . According to some embodiments the upper receiver  1225  may be removably coupled with the hand guard  1220 . According to some embodiments the hand guard  1220  may be removably coupled with the barrel  1215 . 
     According to some embodiments presently disclosed, the firearm  1200  uses a blowback system of operation. Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas crated by the ignition of the propellant charge. 
     Referring to  FIGS. 46-48 , the firearm  1200  comprises a removable side charging handle  1201  according to some embodiments presently disclosed. According to some embodiments presently disclosed, the firearm  1200  comprises the side charging handle  1201  coupled with the bolt carrier assembly  1240  as described below. According to some embodiments presently disclosed, the side charging handle  1201  protrudes from the upper receiver  1225  ( FIGS. 68-69 ). 
     According to some embodiments presently disclosed, the firearm  1200  may also comprise the forward charging system  30  as described above. 
     According to some embodiments presently disclosed, the firearm  1200  comprises a bolt carrier assembly  1240  ( FIGS. 70-72 and 81-82 ). According to some embodiments presently disclosed, the bolt carrier assembly  1240  is movable between a first (i.e. locked) position (shown in  FIGS. 68 and 81 ) and a second (i.e. unlocked) position (shown in  FIGS. 69 and 82 ). According to some embodiments presently disclosed, the bolt carrier assembly  1240  is movable between a first (i.e. locked) position (shown in  FIGS. 68 and 81 ) and a second (i.e. unlocked) position (shown in  FIGS. 69 and 82 ) by the side charging handle  1201 . 
     The bolt carrier assembly  1240  comprises a bolt carrier  1301 , an extractor  1302 , a cam pin  1303 , a firing pin  1304 , a carrier key  1245  ( FIG. 70 ). The bolt carrier assembly  1240  supports and positions the bolt carrier  1301 . The first (locked) position is position in which the bolt carrier assembly  1240  has positioned the bolt carrier  1301  for firing ammunition through the barrel  1215  ( FIG. 81 ). Referring to  FIG. 81 , according to some embodiments, the first (locked) position is position in which the bolt carrier assembly  1240  is locked into battery. The second (unlocked) position is any position other than the first (locked) position ( FIG. 82 ). 
     According to some embodiments presently disclosed, the side charging handle  1201  is configured to move the bolt carrier assembly  1240  from the first (locked) position to the second (unlocked) position. According to some embodiments presently disclosed, the firearm  1200  also comprises the forward charging system  30  as described in detail above. According to some embodiments presently disclosed, the firearm  1200  also comprises the forward charging system  30  as described in detail above, wherein the forward charging system  30  and the side charging handle  1201  are configured to move the bolt carrier assembly  1240  from the first (locked) position to the second (unlocked) position. 
     Referring to  FIGS. 81-82 , according to some embodiments presently disclosed, the lower receiver  1226  comprises openings for accepting the internal mechanisms required to operate the firearm. For example, the lower receiver  1226  may comprise an opening  1281  configured to accept an ammunition magazine (not shown) and associated hardware to direct rounds loaded within the magazine into a chamber in an upper receiver  1225 . The lower receiver  1226  may also comprise an opening  1282  configured to accommodate a firing mechanism (i.e. standard trigger group). According to some embodiments, the firing mechanism (i.e. standard trigger group) comprises a trigger mechanism  583  and a hammer mechanism  584 . 
     Referring to  FIGS. 68-69 and 81-82 , according to some embodiments presently disclosed, the lower receiver  826  comprises a bolt hold open  1285 , an opening  1286  configured to accommodate the bolt hold open  1285 . Referring to  FIGS. 81-82 , according to some embodiments presently disclosed, the opening  1282  is separated from the opening  1286  by a wall  2503 . 
     Referring to  FIG. 70 , according to some embodiments presently disclosed, the carrier key  1245  is removably coupled with a top portion of the bolt carrier  1301 . One or more fasteners  1250  may be used to couple the carrier key  1245  with the bolt carrier assembly  240 . The one or more fasteners  1250  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. 
     According to some embodiments presently disclosed, the carrier key  1245  comprises a surface  1260 . According to some embodiments presently disclosed, the surface  1260  comprises a through aperture  1266  configured to accommodate a recoil spring guide rod  567  described in more detail below. According to some embodiments, the through aperture  1266  is a through-opening. 
     Referring to  FIGS. 71-72 , according to some embodiments presently disclosed, the firearm  1200  comprises the recoil spring guide rod  567 , the recoil spring  568 , and the plug  569  as described in detail above and below. 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  is configured to go through the aperture  1266  and into the aperture in the upper receiver  1225 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  is configured to abut the plug  569 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  1245  and the plug  566 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  has a diameter that is larger than the diameter of the rest of the recoil spring guide rod  567 . According to some embodiments presently disclosed, the recoil spring guide rod  567  passes through the recoil spring  568  and the recoil spring  568  is positioned between the carrier key  545  and larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . 
     According to some embodiments, the bolt carrier assembly  1240  is configured to slide along the recoil spring guide rod  567  between the first (i.e. locked) position and a second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s forward portion  571  always resides in the aperture of the upper receiver  1225 . 
     According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the upper receiver  1225 . According to some embodiments presently disclosed, the recoil spring guide rod  567 &#39;s rear portion  572  does not extend beyond the lower receiver  1226 . 
     According to some embodiments, the bolt carrier assembly  1240  does not extend beyond the lower receiver  1226  when in the second (i.e. unlocked) position. 
     According to some embodiments presently disclosed, moving the bolt carrier assembly  1240  towards the second (unlocked) position compresses the recoil spring  568  between the bolt carrier assembly  1240  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  1240  compresses the recoil spring  568  between the bolt carrier assembly  1240  and the plug  569 . According to some embodiments presently disclosed, applying a first force to the bolt carrier assembly  1240  compresses the recoil spring  568  between the bolt carrier assembly  1240  and the larger diameter of the recoil spring guide rod  567 &#39;s rear portion  572 . Removing the first force causes the compressed recoil spring  568  to move the bolt carrier assembly  1240  towards the first (locked) position. 
     According to some embodiments presently disclosed, the upper receiver  1225  comprises an aperture configured to accommodate the bolt carrier assembly  1240 , the recoil spring  568 , and the recoil spring guide rod  567 . According to some embodiments presently disclosed, the plug  569  abuts the upper receiver  1225  to prevent the bolt carrier assembly  1240 , the recoil spring  568 , and the recoil spring guide rod  567  from being removed from the upper receiver  1225 . 
     Referring to  FIGS. 68-69 and 81-82 , according to some embodiments presently disclosed, the lower receiver  1226  comprises an upwardly extending lobe  1287 . According to some embodiments, the upwardly extending lobe  1287  is integrally coupled with the lower receiver  1226 . According to some embodiments, the upwardly extending lobe  1287  extends from the lower receiver  1226 . 
     According to some embodiments, the upwardly extending lobe  1287  is used to mount a buttstock (not shown) to the lower receiver  1226 . According to some embodiments, the upwardly extending lobe  1287  comprises a generally circular threaded through-hole. 
     According to some embodiments presently disclosed, the upwardly extending lobe  1287  is configured to accommodate a portion of the bolt carrier assembly  1240  when the bolt carrier assembly  1240  is in the second (unlocked) position. According to some embodiments presently disclosed, the generally circular threaded through-hole is configured to accommodate a portion of the bolt carrier assembly  1240  when the bolt carrier assembly  1240  is in the second (unlocked) position. 
     Referring to  FIGS. 71-72 , according to some embodiments presently disclosed, the firearm  1200  comprises the first end plate  591  and the second end plate  592  as described in more detail above. 
     According to some embodiments presently disclosed, the first end plate  591  prevents the bolt carrier assembly  1240  from being positioned beyond the lower receiver  1226  when the bolt carrier assembly is in the second (unlocked) position. 
     According to some embodiments presently disclosed, the second end plate  592  is coupled with the upwardly extending lobe  1287  with the first end plate  591 . 
     Referring to  FIGS. 71-72 , according to some embodiments presently disclosed, the firearm  1200  comprises the recoil buffer  603  as described above. 
     Referring to  FIGS. 52-53 , according to some embodiments presently disclosed, the firearm  1200  comprises the plug  569  removably coupled with the upper receiver  1225 . 
     Referring to  FIGS. 29, 73 and 75 , according to some embodiments presently disclosed, the bolt carrier assembly  540  comprises a rear surface  3001 . According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  does not extend beyond the wall  2500  and into the opening  582  when the bolt carrier assembly  540  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  does not extend beyond the wall  2500  when the bolt carrier assembly  540  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  is positioned between the opening  586  and the opening  582  when the bolt carrier assembly  540  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  does not extend into the opening  582  when the bolt carrier assembly  540  is in the first (locked) position. 
     According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  does not extend beyond the upwardly extending lobe  587  when the bolt carrier assembly  540  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  does not extend beyond the upwardly extending lobe  587  when the bolt carrier assembly  540  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  extends into the upwardly extending lobe  587  but does not extend beyond the lower receiver  526  when the bolt carrier assembly  540  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  extends into the upwardly extending lobe  587  but does not extend beyond the lower receiver  526  when the bolt carrier assembly  540  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  does not extend beyond the lower receiver  526  when the bolt carrier assembly  540  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3001  of the bolt carrier assembly  540  does not extend beyond the lower receiver  526  when the bolt carrier assembly  540  is at furthest possible position away from the first (locked) position. 
     Referring to  FIGS. 52 and 77 , according to some embodiments presently disclosed, the bolt carrier assembly  840  comprises a rear surface  3002 . According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  does not extend beyond the wall  2501  and into the opening  882  when the bolt carrier assembly  840  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  does not extend beyond the wall  2501  when the bolt carrier assembly  840  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  is positioned between the opening  886  and the opening  882  when the bolt carrier assembly  840  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  does not extend into the opening  882  when the bolt carrier assembly  840  is in the first (locked) position. 
     According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  does not extend beyond the upwardly extending lobe  887  when the bolt carrier assembly  840  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  does not extend beyond the upwardly extending lobe  887  when the bolt carrier assembly  840  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  extends into the upwardly extending lobe  887  but does not extend beyond the lower receiver  826  when the bolt carrier assembly  840  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  extends into the upwardly extending lobe  887  but does not extend beyond the lower receiver  826  when the bolt carrier assembly  840  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  does not extend beyond the lower receiver  826  when the bolt carrier assembly  840  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3002  of the bolt carrier assembly  840  does not extend beyond the lower receiver  826  when the bolt carrier assembly  840  is at furthest possible position away from the first (locked) position. 
     Referring to  FIGS. 67 and 79 , according to some embodiments presently disclosed, the bolt carrier assembly  1040  comprises a rear surface  3003 . According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  does not extend beyond the wall  2502  and into the opening  1082  when the bolt carrier assembly  1040  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  does not extend beyond the wall  2502  when the bolt carrier assembly  1040  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  is positioned between the opening  1086  and the opening  1082  when the bolt carrier assembly  1040  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  does not extend into the opening  1082  when the bolt carrier assembly  1040  is in the first (locked) position. 
     According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  does not extend beyond the upwardly extending lobe  1087  when the bolt carrier assembly  1040  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  does not extend beyond the upwardly extending lobe  1087  when the bolt carrier assembly  1040  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  extends into the upwardly extending lobe  1087  but does not extend beyond the lower receiver  1026  when the bolt carrier assembly  1040  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  extends into the upwardly extending lobe  1087  but does not extend beyond the lower receiver  1026  when the bolt carrier assembly  1040  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  does not extend beyond the lower receiver  1026  when the bolt carrier assembly  1040  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3003  of the bolt carrier assembly  1040  does not extend beyond the lower receiver  1026  when the bolt carrier assembly  1040  is at furthest possible position away from the first (locked) position. 
     Referring to  FIGS. 72 and 81 , according to some embodiments presently disclosed, the bolt carrier assembly  1240  comprises a rear surface  3004 . According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  does not extend beyond the wall  2503  and into the opening  1282  when the bolt carrier assembly  1240  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  does not extend beyond the wall  2503  when the bolt carrier assembly  1240  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  is positioned between the opening  1286  and the opening  1282  when the bolt carrier assembly  1240  is in the first (locked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  does not extend into the opening  1282  when the bolt carrier assembly  1240  is in the first (locked) position. 
     According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  does not extend beyond the upwardly extending lobe  1287  when the bolt carrier assembly  1240  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  does not extend beyond the upwardly extending lobe  1287  when the bolt carrier assembly  1240  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  extends into the upwardly extending lobe  1287  but does not extend beyond the lower receiver  1226  when the bolt carrier assembly  1240  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  extends into the upwardly extending lobe  1287  but does not extend beyond the lower receiver  1226  when the bolt carrier assembly  1240  is at furthest possible position away from the first (locked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  does not extend beyond the lower receiver  1226  when the bolt carrier assembly  1240  is in the second (i.e. unlocked) position. According to some embodiments presently disclosed, the rear surface  3004  of the bolt carrier assembly  1240  does not extend beyond the lower receiver  1226  when the bolt carrier assembly  1240  is at furthest possible position away from the first (locked) position. 
     According to some embodiments, the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) described presently are movable from the first (locked) position to the second (unlocked) position. According to some embodiments presently disclosed, the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) described presently are movable away the first (locked) position to another position. The another position is the furthest possible position away from the first (locked) position that the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) can be moved to. According to some embodiments presently disclosed, the furthest possible position away from the first (locked) position is dependent on the recoil spring  568 . According to some embodiments presently disclosed, the furthest possible position away from the first (locked) position is dependent on a compression property of the recoil spring  568 . According to some embodiments presently disclosed, the furthest possible position away from the first (locked) position is dependent on the plug  569 . According to some embodiments presently disclosed, the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) are prevented from moving past the furthest possible position away from the first (locked) position by the plug  569 . According to some embodiments presently disclosed, the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) are prevented from moving past the furthest possible position away from the first (locked) position by the recoil spring  568 . 
     According to some embodiments presently disclosed, the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) may move to the furthest possible position away from the first (locked) position while firing a firearm. According to some embodiments presently disclosed, the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) may move to the furthest possible position away from the first (locked) position using a side charging handle  1001 ,  1201  as described herein. According to some embodiments presently disclosed, the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) may move to the furthest possible position away from the first (locked) position using the forward charging system  30  as described above 
     Referring to  FIG. 51 , according to some embodiments presently disclosed the recoil spring guide rod  567  comprises an aperture  1800 . The aperture  1800  may be configured to accommodate a portion of a first tool  1805  shown in  FIGS. 83-90 . According to some embodiments presently disclosed, the aperture  1800  is a through hole passing through the rod  567 . According to some embodiments presently disclosed, the aperture  1800  is an indentation in the rod  567 . 
     According to some embodiments presently disclosed, the first tool  1805  is used (i.e. configured) to allow a user of a firearm to at least partially disassemble the firearm. According to some embodiments presently disclosed, the first tool  1805  is used (i.e. configured) to allow a user to remove a bolt carrier assembly  1810  from an upper receiver  1815  as shown in  FIGS. 83-90 .  FIGS. 84-86  do not depict the upper receiver  1815  for ease of reference.  FIGS. 87-90  depict a cutaway of the upper receiver  1815  for ease of reference. 
     The tool  1805  may be inserted into the aperture  1800  of the rod  567  as shown in  FIGS. 83, 84, 87  from the bottom of the upper receiver  1815 . According to some embodiments presently disclosed, once inserted in the aperture  1800 , the user may use the tool  1805  to move the rod  567  towards a handguard  1820  which would cause the recoil spring  568  to be compressed. According to some embodiments presently disclosed, once inserted in the aperture  1800 , the user may use the tool  1805  to move the rod  567  towards the bolt carrier assembly  1810  which would cause the recoil spring  568  to be compressed between the tool  1805  and the bolt carrier assembly  1810  as shown in  FIGS. 85 and 88 . According to some embodiments presently disclosed, once inserted in the aperture  1800 , the user may use the tool  1805  to move the rod  567  away from the plug  569  which would cause the recoil spring  568  to be compressed between the tool  1805  and the bolt carrier assembly  1810  as shown in  FIGS. 85 and 88 . 
     According to some embodiments presently disclosed, once the rod  567  is moved away from the plug  569 , the plug  569  is free to be removed from the upper receiver  1815  as shown in  FIGS. 86 and 89 . According to some embodiments presently disclosed, once the rod  567  is moved away from the plug  569 , the plug  569  is free to be removed from the channel  610  shown in  FIG. 41 . Once the plug  569  is removed from the upper receiver  1815 , the rod  567 , the recoil spring  568  and/or the bolt carrier assembly  1810  may be removed from the upper receiver  1815 . 
     According to some embodiments presently disclosed, the first tool  1805  may also be used (i.e. configured) to allow a user to remove the bolt carrier assemblies ( 540 ,  840 ,  1040 ,  1240 ) from their respective upper receivers. 
     Referring to  FIG. 91 , according to some embodiments presently disclosed a recoil spring guide rod  2567  may be used instead of the recoil spring guide rod  567  as described above. 
     According to some embodiments presently disclosed, the recoil spring guide rod  2567  comprises a channel  2800 . The channel  2800  may be configured to accommodate a portion of the first tool  1805  described above. The channel  2800  may be configured to accommodate a portion of a second tool  2805  shown in  FIGS. 92-100 . According to some embodiments presently disclosed, the channel  2800  is positioned alone the circumference of the rod  2567 . According to some embodiments presently disclosed, the channel  2800  is an indentation in the rod  2567 . 
     According to some embodiments presently disclosed, the tool  1805  or  2805  is used (i.e. configured) to allow a user of a firearm to at least partially disassemble the firearm. According to some embodiments presently disclosed, the tool  1805  or  2805  is used (i.e. configured) to allow a user to remove a bolt carrier assembly  2810  from an upper receiver  2815  as shown in  FIGS. 92-98 .  FIGS. 92-95  depict the upper receiver  2815 .  FIGS. 96-99  do not depict the upper receiver  2815  for ease of reference. 
     The tool  1805  or  2805  may be inserted into the channel  2800  of the rod  2567  as shown in  FIGS. 96-98  from the top of the upper receiver  2815  through an aperture  2817  shown in  FIGS. 92-95 . According to some embodiments presently disclosed, once inserted in the channel  2800 , the user may use the tool  1805  or  2805  to move the rod  2567  towards a handguard which would cause the recoil spring  568  to be compressed. According to some embodiments presently disclosed, once inserted in the channel  2800 , the user may use the tool  1805  or  2805  to move the rod  2567  towards the bolt carrier assembly  2810  which would cause the recoil spring  568  to be compressed between the tool  2805  and the bolt carrier assembly  2810  as shown in  FIGS. 96-98 . According to some embodiments presently disclosed, once inserted in the channel  2800 , the user may use the tool  1805  or  2805  to move the rod  2567  away from the plug  569  which would cause the recoil spring  568  to be compressed between the tool  2805  and the bolt carrier assembly  2810  as shown in  FIGS. 96-98 . 
     According to some embodiments presently disclosed, once the rod  2567  is moved away from the plug  569 , the plug  569  is free to be removed from the upper receiver  2815  as shown in  FIGS. 94 and 98 . According to some embodiments presently disclosed, once the rod  2567  is moved away from the plug  569 , the plug  569  is free to be removed from the channel  610  shown in  FIG. 41 . Once the plug  569  is removed from the upper receiver  2815 , the rod  2567 , the recoil spring  568  and/or the bolt carrier assembly  2810  may be removed from the upper receiver  2815  as shown in  FIG. 95 . 
     According to some embodiments presently disclosed, a plug  2819  is used to cover the aperture  2817 . According to some embodiments presently disclosed, a plug  2819  is used to cover the aperture  2817  and prevent dirt from entering the upper receiver  2815 . According to some embodiments presently disclosed, a plug  2819  is used to cover the aperture  2817  and prevent hot gasses from exiting the upper receiver  2815 . According to some embodiments presently disclosed, the tool  1805  or  2805  may be used to remove the plug  2819  from the upper receiver  2815  and expose the aperture  2817  as shown in  FIGS. 99-100 . 
     Referring to  FIGS. 101-103 , an upper receiver assembly  3100  comprises a forward charging system  3000  (shown in  FIGS. 102-103 ) according to some embodiments presently disclosed. The forward charging system  3000  comprises a charging trolley  3045  and the rod  55  as described above. The forward charging system  3000  may also comprise the return spring  50  as described above. The forward charging system  3000  may also comprise a removable charging handle  3040 . 
     The charging trolley  3045  comprises a forward portion  3060  and a rear portion  3065 . According to some embodiments presently disclosed, the charging handle  3040  is coupled with the charging trolley  3045 &#39;s forward portion  3060 . According to some embodiments presently disclosed, the charging handle  3040  is coupled with the charging trolley  3045  adjacent to the forward portion  3060 . According to some embodiments presently disclosed, the charging trolley  3045  comprises an opening  3075  (shown in  FIG. 102 ) configured to accommodate the charging handle  3040  as shown in  FIG. 103 . The opening  3075  may be a through opening to allow the charging handle  3040  to be inserted on either the right or left side of the charging trolley  3045  as shown in  FIGS. 105-108 . The opening  3075  may be a through opening to allow the charging handle  3040  to be inserted either pointing up or down as shown in  FIGS. 105-108 . The charging handle  3040  may be coupled with the charging trolley  3045  using, for example, a fastener  3070  shown in  FIG. 102 . The fastener  3070  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. 
     According to some embodiments presently disclosed, the charging trolley  3045  comprises an opening  3080  (shown in  FIGS. 102-103 ) and the charging handle  3040  comprises an opening  3085  (shown in  FIG. 102 ). The openings  3080  and  3085  are configured to accommodate the fastener  3070 . A set screw may be fully threaded and does not have any head projecting out of the screw thread. According to some embodiments presently disclosed, the charging handle  3040  is coupled substantially perpendicular to the charging trolley  3045 . According to some embodiments presently disclosed, the charging handle  3040  is coupled at an angle to the charging trolley  3045 . 
     As described above, the rod  55  comprises the forward portion  56  and the rear portion  58 . According to some embodiments presently disclosed, rod  55 &#39;s forward portion  56  is coupled with the charging trolley  3045 &#39;s rear portion  3065  as shown in  FIG. 103 . The rod  55  may be coupled with the charging trolley  3045  using, for example, a fastener  3090  shown in  FIG. 102 . The fastener  3090  may be a pin, a screw, a set screw, a full dog point set screw, or a dogleg set screw. According to some embodiments presently disclosed, the charging trolley  3045 &#39;s rear portion  3065  comprises an opening configured to accommodate rod  55 &#39;s forward portion  56 . According to some embodiments presently disclosed, the charging trolley  3045  comprises an opening  3110  and the rod  55  comprises an opening  105 . The openings  3110  and  105  are configured to accommodate the fastener  3090 . 
     According to some embodiments presently disclosed, the upper receiver  25  comprises a bolt carrier assembly  110  as described above. The bolt carrier assembly  110  is movable between a first (locked) position and a second (unlocked) position. According to some embodiments presently disclosed, the forward charging system  3000  is configured to move the bolt carrier assembly  110  from the first (locked) position to the second (unlocked). 
     According to some embodiments presently disclosed, the charging handle  3040  is positioned to protrude though an opening  3116  of the hand guard  3200  (as shown in  FIGS. 105 and 108 ). According to some embodiments presently disclosed, the charging handle  3040  is positioned adjacent to a barrel. According to some embodiments presently disclosed, the charging handle  3040  is positioned away from the upper receiver  25  as shown in  FIG. 101 . According to some embodiments presently disclosed, the charging base  3040  is positioned away from the upper receiver  25  and towards the front of the firearm and as shown in  FIG. 101 . 
     According to some embodiments presently disclosed, the hand guard  3200  comprises an opening  3124  configured to accommodate a barrel (shown in  FIGS. 101 and 109 ). According to some embodiments presently disclosed, the hand guard  3200  comprises an opening  3125  configured to accommodate the charging trolley  3045 . According to some embodiments presently disclosed, the opening  3124  and/or  3125  are formed during manufacturing of the hand guard  3200 . According to some embodiments presently disclosed, the opening  3124  and/or  3125  are extruded during manufacturing of the hand guard  3200 . According to some embodiments presently disclosed, the opening  3124  and/or  3125  run along the entire length of the hand guard  3200 . According to some embodiments presently disclosed, the opening  3125  runs along a portion of the hand guard  3200 . The charging trolley  3045  is configured to slide within the opening  3125  from a first (rest) position to a second (charging) position and back to the first (rest) position. 
     According to some embodiments presently disclosed, the opening  3125  comprises a circular cross section. According to some embodiments presently disclosed, the opening  3125  comprises a substantially circular cross section. According to some embodiments presently disclosed, the opening  3125  comprises a substantially U-shaped cross section. 
     According to some embodiments presently disclosed, the opening  3125  comprises one or more walls  3126  along the perimeter of the opening  3125 . According to some embodiments presently disclosed, the opening  3125  comprises at least two walls  3126  along the perimeter of the opening  3125 . According to some embodiments presently disclosed, the charging trolley  3045  is configured to slide along the at least two walls  3126  from a first (rest) position to a second (charging) position and back to the first (rest) position. 
     According to some embodiments presently disclosed, the opening  3125  comprises a plurality of walls  3126  defining the perimeter of the opening  3125 . According to some embodiments presently disclosed, the charging trolley  3045  is configured to slide along the plurality of walls  3126  from a first (rest) position to a second (charging) position and back to the first (rest) position. 
     According to some embodiments presently disclosed, the opening  3125  comprises five outer walls  3126  defining the perimeter of the opening  3125 . According to some embodiments presently disclosed, the charging trolley  3045  is configured to slide along the one or more walls  3126  from a first (rest) position to a second (charging) position and back to the first (rest) position. 
     According to some embodiments presently disclosed, moving the charging trolley  3045  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to abut (i.e. engage) the carrier key  115  described above. According to some embodiments presently disclosed, moving the charging trolley  3045  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to engage the carrier key  115  and move the bolt carrier assembly  110  from the first (locked) position to the second (unlocked) position as described above. According to some embodiments presently disclosed, moving the charging trolley  3045  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to move the bolt carrier assembly  110  from the first (locked) position to the second (unlocked) position as described above. According to some embodiments presently disclosed, moving the charging trolley  3045  towards the second (charging) position causes rod  55 &#39;s rear portion  58  to engage the carrier key  115  and move the bolt carrier assembly  110  away from the barrel as described above. 
     According to some embodiments presently disclosed, the charging trolley  3045 &#39;s second (charging) position is position in which the charging trolley  3045  is positioned closer to the upper receiver  25 . According to some embodiments presently disclosed, the charging trolley  3045 &#39;s first (rest) position is position in which the charging trolley  3045  is positioned closer to the front of the firearm and away from the upper receiver  25 . According to some embodiments presently disclosed, the charging trolley  3045 &#39;s second (charging) position is position in which the rod  55  moves the bolt carrier assembly  110  to the second (unlocked) position. According to some embodiments presently disclosed, the charging trolley  3045 &#39;s first (rest) position is position in which the rod  55  allows the bolt carrier assembly  110  to return to the first (locked) position. According to some embodiments presently disclosed, the charging trolley  3045 &#39;s first (rest) position is position in which the rod  55  is positioned away from the carrier key  115 . 
     According to some embodiments presently disclosed, the charging trolley  3045  is moved towards the second (charging) position by applying a first force on the charging handle  3040  towards the second (charging) position. According to some embodiments presently disclosed, the charging trolley  3045  is moved towards the second (charging) position by applying a first force on the charging handle  3040  towards a buttstock located at the rear of the firearm. 
     According to some embodiments presently disclosed, the upper receiver  25  comprises a through opening  150  to allow the rod  55  to pass though and be able to engage the carrier key  115 . 
     According to some embodiments presently disclosed, the rod  55  passes through the return spring  50  that is positioned between the upper receiver  25  and the charging trolley  3045  as shown in  FIG. 103 . According to some embodiments presently disclosed, moving the charging trolley  3045  towards the second (charging) position compresses the return spring  50  between the charging trolley  3045  and the upper receiver  25 . According to some embodiments presently disclosed, applying the first force to the charging handle  3040  compresses the return spring  50  between the charging trolley  3045  and the upper receiver  25 . Removing the first force causes the compressed return spring  50  to return the charging trolley  3045  back to the first (rest) position. According to some embodiments presently disclosed, the return spring  50  prevents the charging trolley  3045  from moving from the first (rest) position towards the second (charging position). According to some embodiments presently disclosed, the return spring  50  prevents the charging trolley  3045  from moving from the first (rest) position towards the second (charging position) during normal operations of the firearm. 
     Referring to  FIGS. 111-116 , an upper receiver assembly  4500  is shown according to some embodiments presently disclosed. The upper receiver assembly  4500  comprises a barrel  4515 , a hand guard  4520  and an upper receiver  4525 . According to some embodiments the upper receiver  4525  is coupled to a lower receiver (not shown). The hand guard  4520  may removably encircle the barrel  4515 . 
     According to some embodiments presently disclosed, the upper receiver assembly  4500  comprises two charging systems. One system is the forward charging system  30  as described above. The forward charging system  30  comprises a charging base  40 , a charging trolley  45 , and a rod  55 . The forward charging system  30  may also comprise a return spring  50 . 
     A second charging system is a rear charging system comprising a T-shaped charging handle  4550 . When the charging handle  4550  is pulled hack towards the buttstock, the operator of the firearm can eject a spent shell casing or an unfired cartridge from a chamber, load a round from the magazine, clear a jam or misfire, move a bolt into battery, and/or release a bolt locked to the rear. 
     According to some embodiments presently disclosed, the upper receiver  4525  comprises the bolt carrier assembly  110 . The bolt carrier assembly  110  is movable between a first (locked) position and a second (unlocked) position. The bolt carrier assembly  110  supports and positions a bolt (not shown). The first (locked) position is position in which the bolt carrier  110  has positioned the bolt (not shown) for firing ammunition through the barrel  515 . The second (unlocked) position is any position other than the first (locked) position. 
     As described above, the forward charging system  30  and/or the T-shaped charging handle  550  are configured to move the bolt carrier assembly  110  from the first (locked) position to the second (unlocked). 
     It is to be understood that the embodiments described above may be implemented on different types of firearms. The embodiments described above may be implemented on firearms using a blowback system of operation, and/or firearm using a direct impingement system of operation, and/or firearm using piston system of operation. Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas crated by the ignition of the propellant charge. Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly into the bolt carrier to cycle the action. Piston system uses gas pressure to mechanically move the bolt carrier to cycle the action. It is also to be understood that the embodiments described above may be implemented on M-16 and Armalite style rifles (ARs). 
     While several illustrative embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternative embodiments are contemplated, and can be made without departing from the scope of the invention as defined in the appended claims. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. The term “plurality” includes two or more referents unless the content clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains.