Abstract:
A bolt carrier for use with the ARI5/MI6 family of firearms is provided. The bolt carrier includes an integrally formed carrier key and spherical strike face surrounded by a cylindrical counterbore made with a downward angle to act against the tilting force imparted by the operating rod of the firearm&#39;s gas operating system. The outer surface of the carrier includes upper and lower running rails that all extend fully to the front face of the carrier to lengthen the carrier&#39;s rail support or bearing surfaces against the receiver.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to self-loading firearms. More particularly, the present invention relates to the operating system of indirect gas-operated firearms in the AR15/M16 series of firearms and specifically the bolt carrier for use in such firearms. 
     2. Description of the Related Art 
     The AR15/M16 family of weapons and their derivatives including indirect gas operated versions, have been in use by the military and civilian population for many years. An essential part of this firearm&#39;s design is the bolt carrier which typically includes a bolt mounted in the carrier for axial sliding movement and rotation, a firing pin slidably mounted within the bolt and bolt carrier for restricted reciprocating axial movement, and a cam pin for producing relative rotation between the bolt and the bolt carrier. 
     The bolt carrier is generally cylindrical in shape with a longitudinally extending circular bore throughout its length. An elongated opening is provided in the top and bottom of the carrier to allow the hammer to extend into the interior of the bolt carrier and strike the firing pin. The rear of the carrier is received within the firearm receiver and the front of the carrier houses the bolt. The upper surface of the carrier immediately adjacent the front face includes a flat shelf for engagement with a charging handle. 
     The top of the carrier in front of the opening is machined to receive a carrier key which operates in conjunction with the operating rod of the firearm&#39;s gas operating system to cycle the bolt action in automatic and semi-automatic operation. A carrier with a separate carrier key that is attached to the carrier with fasteners is set forth in U.S. Pat. No. 7,461,581 (“the &#39;581 patent”), which is owned by the assignee of the present application and is hereby expressly incorporated by reference as if fully set forth herein. This two-part construction necessitates careful machining of both the carrier and the carrier key to ensure a close fit within a narrow tolerance. 
     In a conventional indirect gas operated firearm, the operating rod of the gas operating system contacts the strike face of the carrier key after the weapon is fired and gas pressure displaces the operating rod rearwardly. Because the strike face is above the central axis of the bolt carrier, an undesirable phenomenon known as carrier tilt occurs during the normal operation of the firearm. Carrier tilt can be defined as the rear of the carrier tilting downwardly when the strike face has been contacted by the operating rod, resulting in the rearward movement of the carrier being resisted when the now off-axis carrier strikes the forward leading edge of the receiver extension. Eliminating carrier tilt would be a very desirable attribute. 
     About the exterior of the bolt carrier are a series of longitudinally extending lands or rails, usually four, which make contact with the cylindrical interior surface of the upper receiver of the firearm and serve to align the bolt carrier within the receiver. The rails include two upper rails and two lower rails spaced from one another about the exterior circumference of the bolt carrier. The upper rails extend from the elongated opening to the rear edge of the charging handle engagement shelf. The two lower rails are generally parallel with the upper rails and extend from the elongated opening all the way to the front face of the carrier. 
     Conventionally, the rails are contiguous and held to tight tolerance with the running surfaces in the upper receiver. Firearms such as the Stoner type rifle are very prone to stoppages and malfunctions when sand or dirt works into the receiver. Therefore, a need exists for a rail configuration that supports the carrier while reducing the likelihood of firearm malfunction when exposed to dirt and sand. 
     The rear end of the carrier typically does not contact the inside of the receiver but rather is supported by the longitudinal rails. To further support the carrier against carrier tilt, the rear of the carrier may be provided with a generally cylindrical boss having an outer diameter larger than the main body of the bolt carrier as described in a copending application filed on Oct. 10, 2008, entitled “Automatic Rifle Bolt Carrier with Fluted Boss”, by Jesus S. Gomez and Jason Miller (hereinafter, “the Gomez application”), which is also owned by the assignee of the present application and is hereby expressly incorporated by reference as if fully set forth herein. The boss in the Gomez application has an outer diameter large enough to make contact with the cylindrical inside of the receiver extension to ensure that the carrier centers therein. 
     Firearms based on the ARI5/MI6 family are the primary weapon of choice for military units in the United States and abroad. Highly trained units from all branches of service often find themselves operating in aquatic conditions prior to coming on land. The inability of the ARI5/MI6 series of weapons to be fired when water is present in the operating system puts these military personnel in a compromising position. With the current ARI5/MI6 series of weapons, and their derivatives, the firearm must be drained of all water prior to being discharged. This draining is not convenient or practical for a soldier who may come under fire immediately upon landing on a beach. Such situations are typically referred to as “over the beach operations”. Incorporating features into the operating system which allow the firearm to be immediately discharged upon exit from an aquatic environment would be highly desirable. One such feature is set forth in the Gomez application, namely, a series of longitudinal cuts or flutes spaced about the circumference of the boss to allow for water to pass by the boss. Additional water removal features would also be desirable. 
     It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, one object of the present invention is to overcome the shortcomings in the design of bolt carriers and bolts for self-loading firearms as described above. 
     Another object of the present invention is to overcome the phenomenon of carrier tilt in gas-operated automatic and semi-automatic firearms. 
     Yet another object of the present invention is to provide a bolt carrier for a gas-operated automatic or semi-automatic firearm having an carrier key integrally formed with the carrier to facilitate carrier design and manufacture. 
     A further object of the present invention is to provide a bolt carrier for a gas-operated automatic or semi-automatic firearm in accordance with the preceding objects in which the integral carrier key has a spherical strike face and a cylindrical counterbore which acts against the off-axis force imparted by the operating rod of the firearm&#39;s gas operating system during operation of the firearm to prevent carrier tilt. 
     A still further object of the present invention is to provide a bolt carrier for a gas-operated automatic or semi-automatic firearm in accordance with the preceding objects in which the rear of the carrier includes an enlarged boss as described in the Gomez application that engages the receiver to further reduce carrier tilt. 
     Another object of the present invention is to provide a bolt carrier for a gas-operated automatic or semi-automatic firearm in accordance with the preceding objects in which the boss has a plurality of cuts or flutes formed therein as described in the Gomez application to allow for water transfer, making the firearm safe for use in over the beach operations. 
     Yet another object of the present invention is to provide a bolt carrier for a gas-operated automatic or semi-automatic firearm in accordance with the preceding objects in which the rails on the upper surface of the carrier are extended all the way to the front face of the carrier to further mitigate carrier tilt. 
     A further object of the present invention is to provide a bolt carrier for a gas-operated automatic or semi-automatic firearm in accordance with the preceding objects in which the rails of the carrier have relief or sand cuts that provide a place for dirt and sand to accumulate so that such debris will not jam the firearm. 
     Another object of the present invention is to provide a bolt carrier for a gas-operated automatic or semi-automatic firearm in accordance with the preceding objects in which drain holes are provided in the bottom and rear of the receiver extension to allow water in the receiver extension to escape. 
     Yet another object of the present invention is to provide an improved bolt carrier in accordance with the preceding objects that can be used to upgrade existing weapons in the field without the requirement for any tools. 
     A still further object of the present invention to provide an improved bolt carrier for a rotary bolt action gun that is not complex in structure and which can be manufactured at low cost but yet greatly increases the reliability and safety of the firearm. 
     In accordance with these and other objects, the present invention is directed to a firearm from the AR15/M16 family, or an indirect gas-operated derivative, having a bolt carrier as previously described, with an improved bolt carrier which can be retrofitted to existing firearms of the AR15/M16 family of firearms using an indirect gas-operated system without any modification to the receiver of the firearm or any other part thereof. 
     The bolt carrier has several features that reduce carrier tilt. First, the carrier includes an integrally formed carrier key having a downwardly angled spherical strike face with a cylindrical counterbore to act against the tilting force imparted by the operating rod of the gas operating system. Second, the rear of the carrier includes a boss having a larger diameter relative to the main body of the carrier to ensure that the carrier is centered in the receiver and receiver extension, further mitigating carrier tilt as discussed previously in connection with the Gomez application. Third, the upper rails on the outer circumference of the carrier are extended to the front face of the carrier to provide longer rail support surfaces and still further reduce tilting of the carrier during operation. 
     In addition to reducing carrier tilt, the bolt carrier according to the present invention also includes features that reduce manufacturing costs and improve the robust operation of the firearm in adverse conditions. In particular, the bolt carrier of the instant invention has a carrier key integrally formed with the bolt carrier as one piece. This one-piece construction reduces manufacturing complexity and cost. 
     Further, for over the beach operations, the sides of the boss at the rear of the carrier have cuts or flutes formed therein to allow water to pass as already discussed. According to the present invention, these flutes work in conjunction with drain holes that are provided in the bottom and rear of the receiver extension. Specifically, as the weapon is fired, the bolt carrier moves rearwardly into the receiver extension. Water present in the receiver extension is forced, by the pumping action created by the moving bolt carrier, outwardly through the drain holes in the receiver extension to empty the receiver extension of water. In addition, water can pass through the flutes in the boss to exit the receiver and receiver extension by moving past the carrier as a result of the same pumping action created by the cycling of the bolt carrier during firing. 
     In addition, for improved performance in sandy and dirty conditions, the rails on the forward end of the carrier that contact the receiver have relief or sand cuts formed therein to provide a recess for dirt and dust to accumulate during operation of the firearm so that debris will not jam the weapon. 
     Finally, to improve the durability of the weapon, the operating rod is preferably made of a super alloy with high nickel and cobalt content. 
     These together with other improvements and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a bolt carrier according to the present invention. 
         FIG. 2  is another perspective view of the bolt carrier shown in  FIG. 1 . 
         FIG. 3A  shows the bolt carrier of  FIGS. 1 and 2  with the other components of a firearm in battery. 
         FIG. 3B  is an exploded view of the firearm components shown in  FIG. 3A . 
         FIG. 4  is an end view of the integrally formed carrier key and strike face of the bolt carrier of  FIGS. 1-3 . 
         FIG. 4A  is a cross-sectional view taken along line A-A of  FIG. 4 . 
         FIG. 4B  is an enlarged view of detail B of  FIG. 4 . 
         FIG. 5  is a partial perspective view of the firearm of  FIG. 3  showing the forces exerted on the firearm when the action is first initiated upon firing of the weapon. 
         FIG. 6  shows the firearm of  FIG. 5  after the operating rod, under gas pressure produced by firing, has struck the carrier key and initiated rearward movement of the bolt carrier. 
         FIG. 7  is an upper perspective view of the bolt carrier of  FIGS. 1 and 2  as received within the receiver. 
         FIG. 8  is a lower perspective view of the components shown in  FIG. 7 . 
         FIG. 9A  is a perspective view of the receiver extension of the firearm shown in  FIG. 3 . 
         FIG. 9B  is a perspective bottom view of the receiver extension shown in  FIG. 9A , showing the drain holes therein. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing a preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     As used herein, the word “front” or “forward” corresponds to the end of the bolt carrier where the strike face is located, i.e., to the right as shown in  FIGS. 1 and 2 . The “rear” or “rearward” or “back” corresponds to the direction opposite the end of the bolt carrier where the strike face is located, i.e., to the left as shown in  FIGS. 1 and 2 . The term “battery” refers to the position of readiness of a firearm for firing. 
     As shown in  FIGS. 1 and 2 , the present invention is directed to a bolt carrier generally designated by reference numeral  10 . It will be understood that bolt carrier  10  is intended to be employed with any indirect gas-operated firearm. It will also be understood that bolt carrier  10  is carried by an upper receiver  12  that cooperates with a lower receiver  11  and receiver extension  41  of a gas-operated automatic or semi-automatic firearm, generally designated by reference numeral  13 , as shown in  FIGS. 3A and 3B . As is known, the firearm  13  includes a gas operating system generally designated by reference numeral  42 , and a barrel  43 . The receiver extension is received within the buttstock  49 . 
     In  FIGS. 1 and 2 , the preferred embodiment of the bolt carrier  10  is shown. The bolt carrier  10  includes a hammer clearance slot  14  which permits the hammer (not shown but well known in the art) to extend into the bolt carrier  10  and strike a firing pin (not shown) positioned in bore  16 . 
     The exterior of the carrier includes a door opener  18  which provides room for the door latch (well known in the art) to close, and a cam slot  20  which provides a contained area for the cam pin (not shown) to rotate thus allowing the bolt  22  (see  FIG. 6 ) to move rearwardly and rotate axially in the bolt carrier  10 ; the cam pin retains the bolt  22  within the bolt carrier  10  as is known in the art. One side of the bolt carrier  10  is provided with forward assist notches  24  as is well known in the art. The top of the carrier immediately adjacent the front face  26  thereof has a flat charging handle engagement shelf  28  for a charging handle  82  (see  FIGS. 7 and 8 ), as is also known in the art. 
     The top of the bolt carrier is formed with an integral carrier key  30  having a strike face generally designated by reference numeral  32 . As illustrated in  FIGS. 4 ,  4 A and  4 B, according to the present invention the strike face  32  is spherical and includes a concave dimple  36  with a cylindrical counterbore  38  leading into the dimple. The cylindrical counterbore  38  has a depth of at least about 0.001 inches ranging up to about 0.5 inches, and preferably is about 0.009 inches, and serves to prevent excessive flexing of the operating rod during firearm operation. In particular, the end of the operating rod may be provided with a convex surface generally complementary with the concave dimple. During the self loading process, the operating rod is subjected to considerable stress that can cause the rod to flex. If the rod flexes enough to contact the cylindrical counterbore  38 , the cylindrical shape of the counterbore will act as a support for the rod to prevent further flexing. The outermost edge  37  of the strike face also preferably has a chamfered portion  31  leading into the counterbore as best seen in  FIG. 4B . 
     The strike face  32 , cylindrical counter bore  38 , outermost edge  37  and chamfered portion  31  are all made with a downward angle of between about 0.05° and about 5.0°, and is preferably about 0.3°. Hence, according to a preferred embodiment, the face, counterbore, edge and chamfer are all angled downwardly, with the angle  39  as measured from the outermost edge  37  to the center axis  34  of the carrier bore  16  being between about 89.95° and about 85.0°, as shown in  FIG. 4A . 
     As already noted, the strike face  32  is contacted by the operating rod  40  of the weapon&#39;s gas operating system  42  when the weapon is fired. In sum, when the firearm  13  is fired, gas pressure entering the gas operating system  42  pushes the operating rod  40  rearwardly against the strike face  32  as indicated by arrow  50  shown in  FIG. 5 . Gas vents  52  are located at the limit of the desired operating stroke to bleed off any excess gas, preventing over-stroking. The operating rod  40  delivers a buffered impulse to the bolt carrier  10  via the strike face  32  which carrier then moves rearwardly, rotating the bolt  22  and causing it to unlock and begin the cartridge extraction process. The downward angle of the strike face  32  and counterbore  38  counteracts the off-axis force exerted by the operating rod  40  so that downward tilt of the rear  27  of the bolt carrier  10  within the receiver is prevented. 
     As shown in  FIG. 6 , the bolt carrier  10 , having more mass than the operating rod  40 , continues to move rearwardly after the operating rod “runs out of gas”, so to speak, and returns to battery under spring tension, independently of the bolt carrier motion. The bolt carrier thereafter returns to battery under the spring force of a buffer return spring (not shown) located in the stock. 
     In addition to the benefits of the angled strike face  32  and counterbore  38  in reducing carrier tilt, forming the carrier key  30  integrally with the carrier  10  reduces manufacturing complexity and cost. Particularly, forming the carrier key and the carrier as a single piece eliminates the need for exact machining of separate carrier and carrier key components otherwise needed to ensure a precise fit within close tolerances. With the single-piece construction, manufacture is simplified and manufacturing costs reduced. 
     Preferably, the rear  27  of the bolt carrier  10  is provided with a boss, generally designated by reference numeral  60 , having an outer diameter  62  larger than the main body  64  of the bolt carrier  10  with cuts or flutes  66  therein for water passage, as already discussed herein and in the Gomez application. 
     As shown in  FIGS. 1 ,  2 ,  7  and  8 , the exterior of the bolt carrier  10  is provided with a series of longitudinally extending lands or rails, generally four, that include upper rails  70  and lower rails  72 . The lower rails  72  extend from the front face  26  of the bolt carrier  10  rearwardly for a distance of about one-half the length of the bolt carrier. According to the present invention, the upper rails  70  are made with extensions  74  that extend forwardly to also reach the front face  26  of the bolt carrier as shown in  FIGS. 1 ,  2  and  7 . The extensions  74  lie on either side of the charging handle engagement shelf  28 . The rails  70 ,  72 , in conjunction with the boss  60 , support the front  29  and rear  27  respectively, of the bolt carrier  10  to prevent the bolt carrier from tilting and wearing on the receiver  12  during the normal operation of an M16 or related firearm. 
     Both the upper rails  70  and the lower rails  72 , shown in  FIG. 8 , have debris relief cuts  80  formed therein. These cuts  80  provide a recess which captures any dirt and other debris that enters the receiver as the bolt carrier moves back and forth during firing. By accumulating the dirt, etc. in the recess  80 , the weapon is not stalled by such material but can continue to operate. 
     As noted earlier, the bolt carrier  10  is received within a receiver extension  41  which is shown in isolation in  FIG. 9 . According to a further feature of the present invention, the bottom  15  and rear  17  of the receiver extension  41  are provided with drain holes  45  as shown in  FIG. 9B  for removal of water trapped in the receiver extension during over the beach operations. As noted earlier, as the weapon is fired, the bolt carrier moves rearwardly into the receiver extension  41 . Water present in the receiver extension is forced, by the pumping action created by the reciprocating movement of the bolt carrier, outwardly through the drain holes  45  in the bottom  15  and rear  17  of the receiver extension  41  to empty the receiver extension of water. In addition, water can pass through the flutes  66  in the boss  60  to exit the receiver by moving past the carrier as a result of the same pumping action created by the cycling of the bolt carrier during firing. Hence, a firearm equipped with the water-draining cuts  66  and the receiver extension drain holes  45  can be immediately fired upon exit from an aquatic environment and, in the process, will automatically self-empty the receiver extension of trapped water. 
     Finally, to improve the durability of the weapon, the operating rod  40  is made of super alloy with high nickel and cobalt content. Such construction produces a stronger operating rod that is able to withstand repeated firing, and the considerable stresses associated therewith, over a longer lifespan than conventional rods. The super alloy is a martensitic age hardening iron-based steel alloy, essentially carbon free, with nickel and cobalt as the main alloying elements, preferably in the range of about 15% to about 22% nickel and about 5% to 15% cobalt by weight of the total material composition. The super alloy may also include minor amounts of aluminum, titanium and/or molybdenum as interstitial alloying elements. Preferred compositions have about 17% to about 19% nickel, about 7% to about 12.5% cobalt as the main alloying elements, and about 0.05% to about 0.15% aluminum, about 0.3% to about 1.6% titanium and about 4.6% to about 5.2% molybdenum as interstitial alloying elements, all by weight, with the remainder being iron. Preferred super alloys are available from ATI Allvac of Monroe, N.C., under the names Maraging/VascoMax C-250, Maraging/VascoMax C-300, and Maraging/VascoMax C-350. 
     The foregoing descriptions and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not limited by the dimensions of the preferred embodiment. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.