Abstract:
A bolt assembly for a machine gun according to an exemplary aspect of the present disclosure includes, among other things, a lock interface insert configured to be insertable into a bolt. The lock interface insert includes a main body defining a first engagement surface and a second engagement surface. At least one of the first and second engagement surfaces is configured to selectively engage a portion of a breech lock.

Description:
BACKGROUND 
     This disclosure relates to short recoil weapons, and more particularly to the Browning M2 0.50 caliber (including all variants) and Browning 1919 0.30 caliber machine guns. 
     Short recoil weapons are generally configured to lock a bolt and a barrel together for a predetermined distance to ensure that energy produced by a fired cartridge is dissipated to a safe level prior to opening a breech. Prior to firing, a breech lock disposed in the barrel extension selectively engages a corresponding locking surface of the bolt (also described as the bolt lock interface), locking the bolt and barrel together. After the round is fired, the bolt, barrel extension and barrel travel together the predetermined distance. Then the breech lock disengages the bolt allowing the bolt to accelerate toward the rear of the receiver independently of the barrel. 
     While the bolt and the barrel are locked together and after the weapon is fired, a substantial portion of the recoil force is communicated to the locking surface of the bolt adjacent to the breech lock recess. Accordingly, a common wear point is the locking surface due to high cyclic rates of fire. After the amount of wear of the locking surface exceeds a predetermined wear threshold, the weapon may become dysfunctional or unsafe for use. Accordingly, even though only a small portion of the bolt is worn or distressed beyond allowable limits, the entire bolt is generally discarded. 
     SUMMARY 
     A bolt assembly for a machine gun, according to an exemplary aspect of the present disclosure includes, among other things, a lock interface insert configured to be insertable into a bolt. The lock interface insert includes a main body defining a first engagement surface and a second engagement surface. At least one of the first and second surfaces is configured to selectively engage a portion of a breech lock. 
     In a further non-limiting embodiment of the foregoing bolt assembly, the first and second surfaces are both configured to selectively engage a portion of a breech lock. 
     In a further non-limiting embodiment of either of the foregoing bolt assemblies, the bolt includes a bolt body having a shaped cavity extending inward from a bottom of the bolt body. The shaped cavity is configured to at least partially receive the lock interface insert. 
     In a further non-limiting embodiment of any of the foregoing bolt assemblies, the lock interface insert and the shaped cavity are configured to form an interference fit. 
     In a further non-limiting embodiment of any of the foregoing bolt assemblies, the lock interface insert includes a pair of outward guides forming a flush and continuous surface with a pair of rails of the bolt. 
     In a further non-limiting embodiment of any of the foregoing bolt assemblies, each of said outward guides defines a bevel for engaging a corresponding channel defined by a barrel extension. 
     In a further non-limiting embodiment of any of the foregoing bolt assemblies, the bolt includes a first material and the lock interface insert includes a second material different from the first material in at least one of hardness and metallurgy. 
     A machine gun, according to an exemplary aspect of the present disclosure includes, among other things, a bolt and a barrel extension. The bolt includes a body defining a shaped cavity and a breech lock recess extending inward from a bottom of the body. The barrel extension includes a breech lock disposed within an inner cavity defined by the barrel extension. The breech lock includes a bolt engagement surface selectively received into the breech lock recess for selectively minimizing axial movement of the bolt with respect to the barrel extension. The machine gun includes a lock interface insert at least partially inserted into the shaped cavity. The lock interface insert includes a main body and a pair of outward guides extending from the main body and adjacent to a pair of rails of the bolt. The lock interface insert defines a first engagement surface and a second engagement surface. At least one of the first and second surfaces is configured to selectively engage a portion of the breech lock. 
     In a further non-limiting embodiment of the foregoing machine gun, the first and second surfaces of the lock interface insert are both configured to selectively engage a portion of the breech lock. 
     In a further non-limiting embodiment of either of the foregoing machine guns, the lock interface insert and the shaped cavity of the bolt are configured to form an interference fit. 
     In a further non-limiting embodiment of any of the foregoing machine guns, the bolt includes a first material and the lock interface insert includes a second material different from the first material in at least one of hardness and metallurgy. 
     In a further non-limiting embodiment of any of the foregoing machine guns, each of the outward guides defines a bevel for engaging a corresponding channel defined by the barrel extension. 
     A method of repairing a bolt assembly according to another exemplary aspect of the present disclosure includes, among other things, removing a portion of material adjacent to an engagement surface of a bolt to define a shaped cavity. The method also includes the step of providing a lock interface insert having a shape sized to fit a portion of the shaped cavity. The lock interface insert includes a main body defining a first engagement surface and a second engagement surface. At least one of the first and second surfaces is configured to selectively engage a portion of a breech lock. The method also includes the step of inserting the lock interface insert at least partially within the shaped cavity. 
     These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a prior art machine gun. 
         FIG. 2  is a bottom view of a bolt of the prior art machine gun of  FIG. 1 . 
         FIG. 3  is a partial side view of the bolt of the prior art machine gun of  FIG. 1 , the bolt in an installed and unlocked position. 
         FIG. 4  is a partial side view of a worn surface of the bolt of the prior art machine gun of  FIG. 3 . 
         FIG. 5  is a bottom view of a lock interface insert installed in a bolt. 
         FIG. 6  is a perspective view of the bolt and the lock interface insert of  FIG. 5  in an uninstalled position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a perspective view of prior art machine gun  10 , and more particularly an M2 0.50 caliber machine gun. The machine gun  10  includes a receiver  12  disposed at a first weapon end  15  and a barrel  14  disposed at a second weapon end  17 . The receiver  12  includes a chamber  13  for receiving a bolt and a barrel extension  16  (shown in  FIG. 3 ). The components of the machine gun  10  are well known. 
       FIG. 2  illustrates a bottom view of a bolt  18  of a prior art machine gun  10 . The prior art bolt  18  includes a first bolt end  27  and a second bolt end  29 . The bolt  18  is configured to be partially received in a barrel extension  16  (not shown). The bolt  18  includes a pair of rails  31  extending outward from a pair of lateral sides  24  between the first and second bolt ends  27 ,  29 . The rails  31  include an upper surface  41  and a lower surface  43  each parallel to a bottom  20  and a top  22  of the bolt  18 . The rails  31  are configured to be slideably received in a pair of corresponding channels of the barrel extension  16  (not shown). The bolt  18  also defines a breech lock recess  30  extending inward from the bottom  20  of the bolt  18  for receiving a breech lock  26  (shown in  FIG. 3 ). 
       FIG. 3  illustrates a partial side view of the bolt  18  and barrel extension  16  installed in the receiver  12 . The breech lock  26  is disposed within an inner cavity  28  defined by the barrel extension  16 . The breech lock  26  is free to move within the inner cavity  28  in a direction C. A receiver  12  includes a ramp  36  with a breech lock cam  37  for engaging a locking cam  35  of the breech lock  26 . During counter-recoil, the barrel extension  16  moves in a direction B with respect to the ramp  36 , causing the breech lock  26  to engage the breech lock cam  37 . The breech lock  26  extends upward in the direction C toward the breech lock recess  30 . The breech lock  26  engages the lock interface  32  of the bolt  18  adjacent to the breech lock recess  30 , causing the bolt  18  and the barrel extension  16  to lock together. 
     When the machine gun  10  is fired, a portion of a recoil force F is absorbed by a barrel buffer spring  40  and a driving rod spring  42 . However, a significant amount of the recoil force F is communicated to the lock interface  32  while the bolt  18  is locked to the barrel extension  16  by the breech lock  26 . Additionally, the recoil force F causes the bolt  18  to be driven in a slightly diagonal direction D along a bolt engagement surface  33  of the breech lock  26  when the bolt  18  and the barrel extension  16  are locked together. Accordingly, the lock interface  32  begins to wear as the machine gun  10  fires (shown in  FIG. 4 ). After the amount of wear of the lock interface  32  exceeds a certain threshold, the operation of the machine gun  10  becomes unreliable. The operation of the machine gun  10  is well known. 
       FIG. 5  illustrates a bottom view of a bolt  118  and a lock interface insert  150  in an installed position.  FIG. 6  illustrates a bottom perspective view of a portion of the bolt  118  and the lock interface insert  150  of  FIG. 5  with the lock interface insert  150  in an uninstalled position. In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding original elements. 
     As shown in  FIG. 6 , the bolt  118  defines a shaped cavity  145  for receiving a portion of the lock interface insert  150 . The shaped cavity  145  extends between a forward surface  146  and a rear surface  148  of the bolt  118  along a horizontal axis H and adjacent to the breech lock recess  130 . The forward surface  146  defines a forward angle A F  and the rear surface  148  defines a rear angle A R  with respect to a floor  149  of the shaped cavity  145 . Each of the angles A F , A R  is generally acute. The floor  149  extends at least partially between the upper and lower surfaces  141 ,  143  of the rails  131 , which serve to guide the bolt&#39;s  118  movement with respect to the barrel extension  16 . 
     The lock interface insert  150  includes a main body  152 . The main body  152  includes a first insert surface  154  configured to form a flush and continuous surface with the bottom  20  the bolt  118  (shown in  FIG. 5 ) to engage the receiver  12 . The main body  152  includes a second insert surface  156  substantially parallel to the first insert surface  154  and adjacent to the floor  149  of the bolt  118  when the lock interface insert  150  is placed within the shaped cavity  145 . The main body  152  includes a pair of first sides  160  opposite each other and adjacent to the first and second insert surfaces  154 ,  156 . The first sides  160  are configured to form a flush and continuous surface with the lateral sides  124  of the bolt  118  (shown in  FIG. 5 ). 
     The main body  152  includes a front engagement surface  168  and a rear engagement surface  170  opposite each other for selectively engaging the breech lock  26 . The front and rear engagement surfaces  168 ,  170  are disposed between the first and second insert surfaces  154 ,  156 . The front engagement surface  168  is generally oriented at the forward angle A F  and the rear engagement surface  170  is generally oriented at the rear angle A R  with respect to the second insert surface  156 . The front engagement surface  168  is configured to be substantially parallel to the forward surface  146  of the bolt  118 , and the rear engagement surface  170  is configured to be substantially parallel to the rear surface  148  of the bolt  118 . The rear engagement surface  170  may be configured to be substantially parallel to the bolt engagement surface  33  to redirect a portion of the recoil force F (shown in  FIG. 3 ) perpendicularly from the rear engagement surface  170  and into the bolt engagement surface  33  of the breech lock  26 . 
     As shown in  FIG. 5 , a cross section of the lock interface insert  150  is generally trapezoidal. The forward and rear angles A F , A R  of the shaped cavity  145  may be substantially equal to each other and generally acute. This allows the lock interface insert  150  to be held captive in the shaped cavity  145  by the forward and rear surfaces  146 ,  148  of the bolt  118  and minimizes the possibility that the lock interface insert  150  may become dislodged during operation of the machine gun  110 . As shown in  FIG. 6 , the lock interface insert  150  is symmetrical along the horizontal axis H and can be inserted into the shaped cavity  145  with either the front or rear engagement surfaces  168 ,  170  facing the breech lock  26 . However, other shapes and configurations of the lock interface insert  150  are contemplated. 
     The lock interface insert  150  includes a pair of outward guides  157  extending outward from the main body  152  along the horizontal axis H. The outward guides  157  are adjacent to the second insert surface  156  of the main body  152  and form a flush and continuous surface with the rails  131  of the bolt  118  when the lock interface insert  150  is installed in the shaped cavity  145 . Each of the outward guides  157  may include a pair of bevels  172  for realigning the lock interface insert  150  within the shaped cavity  145  along the horizontal axis H. Realignment occurs by engagement of the bevels  172  with an interior surface of the corresponding channels (not shown) of the barrel extension  16 . The bevels  172  also facilitate the insertion of the lock interface insert  150  into the shaped cavity  145 . The outward guides  157  may be integrally formed with the main body  152 . 
     The shaped cavity  145  and the lock interface insert  150  may be configured to form an interference fit when lock interface insert  150  is slide fitted along the horizontal axis H. Accordingly, no fasteners are required to secure the lock interface insert  150  within the shaped cavity  145 . The outward guides  157  also keep the lock interface insert  150  locked in place. 
     The lock interface insert  150  can be formed by machining, forging, casting or other methods depending on materials used and fitting specifications. The lock interface insert  150  may be formed from a second material including steel, alloy or other metals depending on military specifications and other requirements. The second material of the lock interface insert  150  may have a greater hardness than a first material of the bolt  118 . The second material of the lock interface insert  150  may also be different from the first material of the bolt  118  in metallurgy. Forming the bolt  118  and the lock interface insert  150  from different materials allows each of the components to be separately optimized according to performance requirements, cost and other parameters. 
     Installation of the lock interface insert  150  is as follows. A portion of the prior art bolt  18  adjacent to the lock interface  32  (shown in  FIGS. 2-4 ) is removed to define the shaped cavity  145  (shown in  FIG. 5 ). Removal of the portion of the prior art bolt  18  may be performed by methods generally known in the art including machining. In another embodiment, the shaped cavity  145  is formed during the manufacturing process. Thereafter, the lock interface insert  150  is inserted into the shaped cavity  145  along the horizontal axis H. The lock interface insert  150  may be press fit into the shaped cavity  145  with a conventional insertion tool (not shown). 
     When the rear engagement surface  170  wears beyond the predetermined wear threshold, the operator may reverse the orientation of the lock interface insert  150  by removing the lock interface insert  150  from the shaped cavity  145 , rotating the lock interface insert  150  about a rotational axis R (shown in  FIG. 6 ), and reinserting the lock interface insert  150  into the shaped cavity  145  with the front engagement surface  168  adjacent to the breech lock  26  (shown in  FIG. 5 ). In this way, the advantage of a lock interface insert feature may be extended. Additionally, a sufficient amount of the rear engagement surface  170  is configured to extend below the breech lock recess  130  (shown in  FIG. 5 ) even though a portion of the surface  170  is worn. The remaining portion of the rear engagement surface  170  is able to contact the forward surface  146  of the bolt  118  when the lock interface insert  150  is rotated to retain the lock interface insert  150  within the shaped cavity  145 . The operator may discard the lock interface insert  150  to be replaced by another lock interface insert once both the front and rear engagement surfaces  168 ,  170  are worn. 
     Accordingly, the lock interface insert  150  provides several benefits over the prior art bolt  18 . Only the lock interface insert  150  is discarded after the surfaces  168 ,  170  are worn beyond a predetermined wear threshold rather than the entire bolt  18 . The bolt  118  is field reparable by replacement of the lock interface insert  150 . Accordingly, a lower quantity of bolts may be kept in inventory and the repair time of the bolt is reduced. Additionally, the front and rear engagement surfaces  168 ,  170  of the lock interface insert  150  provide two separate wear surfaces, prolonging the duration between servicing of the bolt  118 . 
     Although the different embodiments have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the embodiments in combination with features or components from another one of the embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiments may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.