Abstract:
An adjustable volume gas piston system for a pneumatic reloading firearm includes a gas block having an anchoring portion for anchoring along the barrel. The gas block also includes a chamber portion in pneumatic connection with the barrel. The chamber portion has one end pointing toward the muzzle and another end pointing away from the muzzle. A plug having a bore is affixed to the chamber portion at the forward end. The second end has an opening to allow travel of a gas pin but retains a gas pin head in the chamber portion, biasing it toward the first end. Upon firing the firearm, the volume of the bore causes a pressure delay on the gas pin head, thereby delaying the timing of pneumatic reloading.

Description:
[0001]    This application claims the benefit of the priority filing date of U.S. provisional application No. 61/920,454, filed on Dec. 23, 2013. 
     
    
     BACKGROUND 
       [0002]    Gas-operated automatic reloading systems for firearms are known in the art. Typically, these systems divert a portion of high pressure gas generated from firing, using it to eject the bullet casing and chamber a new cartridge. Gas blocks are used to control the portion of gas used by the reloading system. Since unregulated pressure can destroy firearm components, gas blocks limit the amount of gas traveling into the reloading system to a predetermined level. Some gas blocks are adjustable, allowing users to change the quantity of gas as firing characteristics change due to altering the type of ammunition, or carbon and other material building up in the firearm form repeated firing. 
         [0003]    Typical gas-operated automatic reloading systems port highly pressurized gas through a gas block and tube, bringing it to impinge directly on the bolt carrier, providing the energy necessary for the carrier to eject the spent casing and chamber a new cartridge. These direct impingement systems must be cleaned frequently. Gasses generated from firing have high concentrations of carbon, sulfates, and other materials that form accretions on firearm parts, adversely affecting firing characteristics. 
         [0004]    Gas piston automatic reloading systems are used as an alternative to avoid contaminating the parts of the firearm. Piston systems employ a gas piston (also known as a ‘gas pin’) that bridges the gas block and the upper receiver. Upon firing, gas travelling into the gas block impinges immediately on a piston head of the gas pin, pushing the gas pin into the receiver to activate the reloading action. In this manner, gas piston systems avoid fouling internal components of the firearm, but can present a timing problem. 
         [0005]    When a cartridge is fired, extremely high temperature and pressure gas generated between the bullet and the casing cause the casing to deform and swell in the chamber. Using softer, thermal conducting metals such as brass for casings help prevent them from lodging in the chamber, but require a brief dwell time allowing a spent casing to cool and shrink before it can be ejected. In direct impingement systems, the brief lag as sufficient pressure builds across the system to move the bolt carrier provides sufficient dwell time. In gas piston systems, the immediacy of the gas acting on the piston head and resulting mechanical reloading movement sometimes fails to allow sufficient dwell time, resulting in a jammed system. 
         [0006]    It is therefore an object of the present invention to provide a gas piston system that avoids residue contamination from firing gases, but also provides sufficient dwell time to avoid malfunctions. Another object of the invention is to provide an adjustable volume gas block that allows a user to adjust the dwell time of the reloading system to a desired timing. Another object of the invention is to provide an adjustable volume gas block integrating dwell time adjustments and gas pressure adjustments. These and other objects are more fully developed in the following description claim and drawings. 
       SUMMARY 
       [0007]    An adjustable volume gas piston system for a pneumatic reloading firearm, preferably having an elongated barrel with a muzzle is disclosed. The primary component of the system is a gas block. The gas block includes an anchoring portion that anchors along the barrel, preferably surrounding the barrel. Anchoring pins may be included at the bottom of the anchoring portion in one embodiment, and in another, notches on the barrel may ensure the anchoring portion stays in position. 
         [0008]    The gas block also includes a chamber portion, preferably above the anchoring portion. The chamber portion is in pneumatic connection with the barrel, allowing gasses from firing the firearm to travel from the interior of the barrel into the chamber portion. Preferably, the chamber portion has a first end toward the muzzle and a second end away from the muzzle. In this manner, the chamber is oblong, oriented in the direction and at the position of a gas pin of the reloading system. 
         [0009]    The first end of the chamber portion is open and adapted to receive a plug. The plug includes a bore and is therefore predominantly hollow, thereby forming a chamber in the chamber portion. The plug is affixed to the chamber at the first end in a manner that prevents it from becoming dislodged when the firearm is fired. The second end includes an opening that receives the gas pin. The gas pin preferably includes a gas pin head that is retained in the chamber portion, in one embodiment because the gas pin head is to large to travel through the opening, and biased toward the first end. A spring located in the chamber portion between the opening and the gas pin head may serve as a biasing mechanism. 
         [0010]    Upon firing the firearm, the volume of the bore produces a pressure delay on the gas pin head. The delayed pressure results in a slight timing differential between firing and activation of the gas pin and pneumatic reloading. An important feature of the chamber portion of the gas block is that it is adjustable, thereby rendering the volume of the chamber portion and the timing differential adjustable. The principal way this adjustability is accomplished is by rendering the plug able to move relative to the chamber portion. In one embodiment the plug has threads that rotatably engage complimentary threads on the chamber portion. In this embodiment, the plug may closely resemble a screw having a head for engaging a fastening mechanism that turns the plug, a series of threads near the shoulder of the head, and an enlarged hollow plug body that forms part of the chamber in the chamber portion. 
         [0011]    Adjusting the position of the plug relative to the chamber portion changes the volume of the chamber portion. Because the plug is movable, and due to pressures created by vibration and pressurized gas entering the chamber portion, over the course of firing several rounds the plug may have a tendency to change its orientation, thereby altering the volume of the chamber portion. To solve this problem, the plug preferably includes a biased stop mechanism to preserves the plug&#39;s position and thereby the volume of the chamber portion after positioning the plug to create a predetermined volume. 
         [0012]    Preferably the biased stop mechanism is a bearing pressed into a biased position on the plug and a complimentary seat for the bearing on the gas block. In one embodiment, for ease of manufacturing, a bore is created through the head of the plug. The bore is sized to accommodate a bearing cylinder. The bearing is retained in the cylinder along with a spring that pushes the bearing to an open end of the cylinder. By inserting the cylinder a certain distance into the bore, a hemispherical portion of the bearing will extend away from the head of the bore. 
         [0013]    In this embodiment, the gas block includes a screw set adjacent the plug head. The screw set includes a seat to receive the bearing. In this manner, as the plug head and bearing are rotated causing the bearing to encounter the screw set, the bearing will ‘snap’ into the seat, thereby retaining the plug in its position. In another embodiment the timing of the threads on the plug may be set so that when the plug is adjusted to its maximum point of insertion into the chamber portion, the bearing aligns with the seat. 
         [0014]    When loosening the plug to adjust the volume of the chamber portion and the timing of the automatic reloading system, the bearing will periodically seat in the screw set, allowing users to set the gas block at a variety of pressures. In order to provide a safety, should firing vibration and pressure cause the bearing to unseat itself from its position, the screw set may include a second seat for catching the bearing and holding it in position prior to adjustment by a user. 
         [0015]    The bore in the plug accounts for part of the gas chamber in the chamber portion. The remainder of the chamber is made up of the gas pin head and any space between the plug and the gas pin head. In one embodiment, the gas pin head may be biased to abut the plug. Preferably, the relationship between the chamber portion and the gas pin head is not a pneumatic seal and some minimal quantity of gasses are capable of travelling past the gas pin head upon firing. To introduce turbulence into gas travelling along the gas pin head, circumferential channels may be incorporated into the gas pin head. In another embodiment, the gas pin head may have a concave surface facing the bore to enlarge the chamber. 
         [0016]    The gas pin head is locked into the chamber portion by an opening in the second end that only permits travel of the shaft of the gas pin. Preferably, the opening may include smaller cut-outs or other openings to allow gasses to pass between the gas pin head and the chamber portion, thereby exiting out the second end. The cut-outs or openings on the second end are not the primary exit for gasses produced by firing however. In one preferred embodiment, an exhaust port may be located direction on the chamber portion. 
         [0017]    Typically the exhaust port will be obscured by the gas piston head prior to firing, either covered by the gas piston head itself, or located between the gas piston head and the second end. When the gas piston head is pushed toward the second end upon firing, the gas piston head will clear the exhaust port allowing pressurized gasses to exit the gas block. The other means for gas to exit the gas block is to travel back down into the barrel. To adjust the gas quantity and pressure travelling into the gas block upon firing, the gas block may also include an impinging screw between the barrel and the chamber portion for closing the pneumatic connection. 
         [0018]    In order to adjust an automatic reloading firearm, including a gas pin and barrel, a gas block is first provided, the gas block having an anchoring portion and also having a chamber portion that defines a chamber. The gas block is installed on the barrel in a manner providing a pneumatic communication through the gas block between the chamber and the barrel. The chamber is preferably open at an end toward the barrel muzzle, and a plug having a bore is inserted into the open end of the chamber. Preferably the bore in the plug also defines a chamber. Prior to inserting the plug, a user preferably inserts a gas pin having a gas pin head into the chamber, such that the shaft of the gas pin extends through an opening in a second end of the chamber portion opposite the first end. Once the gas pin and plug are adjusted, the firearm may be fired, thereby causing a delay in the automatic reloading action of the gas pin. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0019]      FIG. 1  is a side view of a first embodiment adjustable volume gas block installed on a firearm. 
           [0020]      FIG. 2  is a perspective view of an adjustable volume gas block installed on the firearm barrel. 
           [0021]      FIG. 3  is an exploded view of a post screw and washers. 
           [0022]      FIG. 4  is a cut-away view of an adjustable volume gas block with an expanded chamber volume. 
           [0023]      FIG. 5  is a cut-away view of an adjustable volume gas block with a reduced chamber volume. 
           [0024]      FIG. 6  is an exploded view of the first embodiment adjustable volume gas block. 
           [0025]      FIG. 7  is a side view of a second embodiment gas block and gas piston system installed on an automatic reloading firearm. 
           [0026]      FIG. 8  is an enlarged side view of the second embodiment gas block. 
           [0027]      FIG. 9  is a perspective view of a chamber screw according to the second embodiment. 
           [0028]      FIG. 10  is a perspective view of a cylinder having a biased bearing mechanism. 
           [0029]      FIG. 11  is a front partial cut-away view of the second embodiment gas block. 
           [0030]      FIG. 12  is an exploded view of the second embodiment gas block. 
           [0031]      FIG. 13  is a cut-away view of the second embodiment adjustable volume gas block with an expanded chamber volume. 
           [0032]      FIG. 14  is a cut-away view of the second embodiment adjustable volume gas block with a reduced chamber volume. 
           [0033]      FIG. 15  is a cut-away side view of a gas pin of the second embodiment adjustable gas block impinging on the tombstone of an automatic reloading firearm. 
           [0034]      FIGS. 16A ,  16 B, and  16 C are cut away side views of chamber screws having different bore sizes. 
           [0035]      FIG. 17  is a side view of the second embodiment adjustable volume gas block covered by a hand guard on a firearm. 
       
    
    
     REFERENCE NUMBERS 
       [0000]    
       
         
           
               10 . First Embodiment Gas Block 
               12 . Firearm 
               14 . Anchoring Portion 
               16 . Barrel 
               18 . Chamber Portion 
               20 . Gas Piston 
               22 . Set Screw 
               24 . Gas Passage 
               26 . Bearing Mechanism 
               28 . Bearing 
               30 . Longitudinal Slots 
               32 . Post Screw 
               34 . Screw Head 
               36 . Slot 
               38 . Threaded Portion 
               40 . Slanted Shoulder 
               42 . Post 
               44 . Washers 
               46 . Retainer 
               48 . Piston Head 
               50 . Concave portion 
               52 . Piston Head Slots 
               54 . Chamber Portion Slots 
               52 . Larger Chamber Portion 
               54 . Smaller Chamber Portion 
               56 . Spring 
               58 . Pin 
               100 . Second Embodiment Gas Block 
               102 . Gas Operated Reloading System 
               104 . Gas Pin 
               106 . Tombstone 
               108 . Anchoring Portion 
               110 . Chamber Portion 
               112 . Impinging Screw 
               114 . Chamber Screw 
               116 . Portal 
               118 . Broadened Slot 
               120 . Screw Head 
               122 . Bore 
               124 . Socket 
               126 . Bearing Mechanism 
               128 . Cylinder 
               130 . Open End 
               132 . Retaining Portion 
               134 . Bearing 
               136 . Spring 
               138 . Screw Set 
               140 . Divot 
               142 . Gas Pin Head 
               144 . Channels 
               146 . Concave Face 
               148 . Relief Port 
               150 . Gas Pin Spring 
               152 . Chamber Exhaust 
               154 . Bore 
               156 . Hand Guard 
           
         
       
     
       DESCRIPTION 
       [0092]    Referring to  FIG. 1 , an adjustable volume gas block  10  is shown affixed to a gas-operated reloading firearm  12 . The gas block  10  comprises an anchoring portion  14  which fits around the barrel  16  of the firearm  12  and is in fluid communication with the interior (not shown) of the barrel  16 . A chamber portion  18 , which comprises an elongated structure, is formed atop the anchoring portion  14 . In a preferred embodiment, the chamber portion  18  extends longitudinally back along the barrel  16  from the anchoring portion  14 . 
         [0093]    Referring to  FIG. 2 , the gas block  10  comprises two mechanisms for controlling the gas pressure coming from the barrel  16 , allowing users to precisely control the action of the gas piston  20  of the firearm  12  when reloading. The first, a bearing mechanism  26  includes a set screw  22  designed to impinge the gas passage  24  (see  FIGS. 4 and 5 ) between the barrel  16  and the chamber portion  18 . The bearing mechanism  26  urges a bearing  28  (see  FIG. 6 ) against longitudinal slots  30  (see  FIG. 6 ) on the set screw  22  to preserve it in a desired position. The second, adjustable volume mechanism includes a post screw  32  anchored in the chamber portion  18  which, with the addition of one or more washers  44  (see  FIG. 3 ), reduces the volume in the chamber portion  18 . 
         [0094]    Referring to  FIG. 3 , the post screw  32  includes a screw head  34 , which preferably includes a conventional engaging mechanism, such as a slot  36  or similar mechanism for engaging a tool (not shown) such as a screw driver. Although a slotted screw head  34  is shown, any type of engaging mechanism allowing the post screw  32  to be turned is contemplated. The post screw  32  also includes a threaded portion  38  for engaging the chamber portion  18  of the gas block  10  and to hold the post screw  32  in position. Preferably, the post screw  32  engages the chamber portion  18  to the front of the gas block  10 , opposite where the gas piston  20  exits the chamber portion  18 . The post screw  32  may also include a slanted shoulder  40  for creating a tight seal against the chamber portion  18 . 
         [0095]    Still referring to  FIG. 3 , the post screw  32  includes a post  42  extending from the screw head  34 , through the chamber portion  18 . The post  42  is substantially narrower than the chamber portion  18  and is adapted to receive one or more washers  44  which will fill the chamber portion  18  once inserted on the post  42 . Optionally, a retainer  46  may be included to hold the washers  44  in place. 
         [0096]    Referring to  FIGS. 4 and 5 , two cross sectional views of the gas block  10  are shown having two different pressure settings. Referring to  FIG. 4 , the post screw  32  has been inserted into the chamber portion  18 , with the threaded portion  38  and slanted shoulder  40  engaging complimentary areas of the chamber portion  18  to form a substantially air-tight seal. The post  42  extends backward, through the chamber portion  18  to engage the piston head  48  of the gas piston  20 . 
         [0097]    Still referring to  FIGS. 4 and 5 , the piston head  48  may include a concave portion  50 , which serves to accommodate the post  42  as well as provide additional chamber area in the chamber portion  18 . Preferably, the piston head  48  also includes piston head slots  52 , which serve to introduce turbulence into gasses travelling around the piston head. Beyond the piston head  48 , chamber portion slots  55  allow excess gasses to escape the chamber portion  18  around the gas piston  20 . With only the post  42  occupying the chamber portion  18  between the piston head  48  and the screw head  34 , a large volume allows more gas to build up in the chamber portion  18  before urging the gas piston  20  to reload the firearm  12 . 
         [0098]    Referring to  FIG. 5 , the set screw  22  is inserted into the chamber portion  18  in the same manner as  FIG. 4 , but with washers  44  installed on the post  42  of the set screw  22 . In this manner, the chamber portion  18  has less volume and allows less gas to build up in the chamber portion  18  before urging the gas piston  20  to reload the firearm  12 . Notably, the interior of the chamber portion  18  includes a larger chamber  52  and a smaller chamber  54 . The larger chamber  52  is sized to accommodate the washers  44 , while the smaller chamber  54  is sized to exclude the washers  44 , and is connected to the gas passage  24 . In this manner, the washers  44  are forced toward the screw head  34  by gas pressure, and are prevented from entering the smaller chamber  54  and occluding the gas passage  24 . The chamber portion  18  also includes an exit portal  55  allowing excess gasses to exit the chamber portion  18   
         [0099]      FIG. 6  shows an exploded view of the gas block  10 . The anchoring portion  14  of the gas block  10  is installed over the barrel  16  of a firearm  12  (not shown), with the chamber portion  18  extending along the barrel  16  to the rear. The bearing mechanism  26  is assembled by inserting the set screw  22  into the gas block  10  and inserting the bearing  28  to engage the longitudinal slots  30 . In one embodiment, the bearing may be held in place by a spring  56 , which is anchored in position by a pin  58 . 
         [0100]    Still referring to  FIG. 6 , the gas piston  20  is inserted into the chamber portion  18 , until the piston head  48  is seated in the smaller chamber  54  (see  FIGS. 4 and 5 ). Preferably a spring (not shown) will be inserted on the gas piston  20  and installed behind the piston head  48  to provide recoil in the chamber portion  18 . With the piston head installed in the smaller chamber  54 , a series of washers  44 , and optionally a retainer  56  may be installed on the post  42  of the post screw  32 . The post screw  32  is then installed in the chamber portion  18  and tightened in position using the threaded portion  38  and slot  36 , such that the slanted shoulder  40  engages a complimentary surface on the chamber portion  18 . 
         [0101]    In operation, the gas block  10  may be assembled without washers. In this manner, the bearing mechanism is set to a desired position. When the firearm is fired, gasses passing through the gas passage enter the chamber portion  18  filling the smaller chamber portion  54  and larger chamber portion  52 . Due to the enlarged chamber portion  18 , and including the concave portion  50  of the piston head  48 , a delay, caused by gas filing the chamber portion  18  will slow activation of the gas piston  20 . 
         [0102]    To reduce the delay, the post screw  32  is removed and one or more washers  44  are installed on the post screw  34 . The washers take up a portion of or all of the larger chamber portion  52 , such that when the firearm is fired, gas more quickly fills the smaller chamber portion  54  and activates movement of the gas piston  20 . Various degrees of pressure may be achieved by only partially filling the larger chamber portion  52  with a desired number of washers  44  and by making corresponding adjustments with the bearing mechanism. 
         [0103]    Referring to  FIGS. 7 through 17 , a second embodiment gas block is shown and described.  FIG. 7  shows the second embodiment gas block  100  affixed to the barrel  16  of the firearm  12  having a gas-operated reloading system  102 . The second embodiment gas block  100  is similar to the first embodiment gas block  10  in that it engages a gas pin  104 , which engages the tombstone  106  of the bolt group for reloading the chamber (not shown). 
         [0104]    Referring to  FIG. 8 , a side view of the second embodiment gas block  100  is shown. Like the first embodiment gas block  10 , the second embodiment gas block  100  includes an anchoring portion  108  and a chamber portion  110 . The second embodiment gas block  100  also includes an impinging screw  112  for impinging the gas passage (not shown) between the barrel  16  and the chamber portion  110 . A chamber screw  114  is installed into the chamber portion  110  of the gas block  100 . The impinging screw  112  is preferably incorporated below the chamber screw  114 . 
         [0105]    Referring to  FIG. 9 , the chamber screw  114  is shown. The chamber screw  114  includes a portal  116  for allowing expelled gas to enter the chamber  110  from the barrel  16  (see  FIG. 8 ). The portal  116  includes a broadened slot  118  on one end. The purpose of the broadened slot  122  is to allow gas to travel from the barrel  16  into the chamber  110  when the chamber screw  114  is in any of its set positions. The chamber screw  114  also includes a screw head  120  with a bore  122  extending through it. 
         [0106]    The screw head  120  preferably includes means for turning or adjusting the position of the screw  114 . In the illustrated embodiment a hexagonal Allen wrench socket  124  is shown, although other mechanisms such as slotted screw heads are contemplated. The screw head  120  also includes a threaded portion  124  for engaging the chamber portion  110  of the gas block  100 . 
         [0107]    Referring to  FIG. 10 , a bearing mechanism  126  is shown. The bearing mechanism  126  comprises a cylinder  128 , which is inserted into the bore  122  on the chamber screw  114  (see  FIG. 9 ). The cylinder  128  is preferably hollow with one open end  130 . The open end  130  of the cylinder  128  includes a retaining portion  132  that retains a bearing  134  in the cylinder  128 . In one embodiment, the retaining portion  132  may present a conical surface. 
         [0108]    Referring to  FIG. 11 , a front view of the second embodiment gas block  100  is shown in partial cut-away view (see  FIG. 8 , cut-away reference  11 ). In this view bearing mechanism  126  is shown incorporated into the bore  122  of the screw head  120 . Shown in this view, a spring  136  is visible biasing the bearing  134  out of the bearing mechanism  126  and against the retaining portion  116 . The bearing mechanism  126  is substantially flush with the screw head  120 , allowing a portion of the bearing  134  to extend past the screw head  120 . 
         [0109]    Still referring to  FIG. 11 , a screw set  138  is proximal the screw head  120  when the chamber screw  114  is installed in the chamber portion  110 . As the biased bearing  134  rotates adjacent the screw set  138 , it is pressed back flush with the screw head  120  under force. The screw set  138  includes divots  140  for accommodating the bearing  134 . In this manner, with the bearing disposed in a divot  140 , it retains the chamber screw  114  in a predetermined position, according to a predetermined chamber portion  110  volume. In the illustrated embodiment, two divots  140  are shown to present a safety. If the bearing  134  is driven under the force of firing from the first divot  140 , the second divot  140  will receive it and prevent the chamber screw  114  from rotating further. Preferably, the timing of the threads (not shown) in the chamber portion  110  and the threads  124  on the chamber screw  126  are such that the bearing  134  will be located in a divot  140  when the chamber screw  114  is in a fully closed position abutting the chamber portion  110 . 
         [0110]    Referring to  FIG. 12 , an exploded view of the second embodiment gas block  100  is shown. The gas pin  104  extends through the chamber  110 , terminating in a gas pin head  142 . The gas pin head  142  is substantially the circumference of the chamber portion  110  interior, but does not create an air tight seal. Rather, several channels  144  are located on the gas pin head  142  to generate turbulence in any gas flow traveling past the gas pin head  142  to provide a cushioning effect. The gas pin head  142  also has a concave face  146 , which increases the total volume of the chamber portion  110 . The chamber  110  also includes a relief port  148 , which allows excess gas to escape the chamber portion  110  once the gas pin head  142  reaches a terminal position at the end of the chamber portion  110  opposite the chamber screw  114 . 
         [0111]    Referring to  FIGS. 13 and 14 , the second embodiment gas block  100  is shown in a condition prior to firing ( FIG. 13 ) and during firing ( FIG. 14 ). Referring to  FIG. 13 , prior to firing, the chamber screw  114  has been turned into the chamber portion  110  to a position of desired pressure. In the illustrated embodiment, the impinging screw  112  has been set to allow gases from firing to travel freely into the chamber portion  110 . The chamber screw  114  has also been set to a predetermined position using the screw set  140 . In the illustrated embodiment, the chamber screw  114  is fully inserted into the chamber portion  110  such that it abuts the gas piston head  142 . When the firearm is fired, gasses enter the chamber and exert pressure according to the arrows. 
         [0112]    Referring to  FIG. 14 , after firing, gasses press against the chamber screw  114 , which is anchored in place, and the gas pin head  142 , forcing the gas pin  104  rearward against the tombstone  106  ( FIG. 7 ). To allow pressure relief, some gas may make its way around the gas pin head  142 , encountering the channels before exiting through the chamber exhaust  152 . The major portion of the gas produced from firing forces the gas pin head  142  backward, compressing the spring  136 , until the gas pin head  142  clears the relief port  148  and exits the chamber  110 . Preferably the relief port  148  is positioned on the chamber  110  such that the gas pin head  142  clears the relief port  148  when the gas pin spring  150  is in a fully compressed position. Any remaining gases in the chamber  110  can also travel back into the barrel  16  and exit before the next round is fired. 
         [0113]    Referring to  FIG. 15 , the opposite end of the gas pin  104  is shown where it engages the tombstone  106  on the firearm  12 . By pushing back the tombstone, the gas pin  104  causes the bolt group (not shown) to move through its operating cycle. Referring to  FIGS. 16A-16C , several sizes of chamber screws  114  are shown with different bore  154  sizes according to user preference. The different bore  154  sizes establish different volumes in the chamber portion  110 . While turning the chamber screw  114  in the chamber  110  allows fine tuning of the gas block  100 , in certain instances a much larger or smaller volume is desired. In these instances, a chamber screw  114  having an enlarged or reduced bore  154  is contemplated. 
         [0114]    Referring to  FIG. 17 , a hand guard  156  is shown attached to the firearm  12  over the gas block  100  (not shown). Due to the reduced size of the gas block  100  compared to other, larger systems, the gas block  100  need not be removed prior to installation of the hand guard  156 . This allows the gas relief characteristics of the gas block  100  to be used even while the hand guard  156  is in place. 
         [0115]    While particular forms of the invention have been illustrated and described, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the full breadth and scope of the appended claims.