Abstract:
To safely and reliably hold the forwardly spring-biased bolt assembly of a machine gun in a rearwardly disposed position within the receiver portion of the gun, a specially designed locking apparatus is mounted on an exterior side surface portion of the receiver. The locking apparatus has a slot therein which is operative to rearwardly receive a bolt pin portion of the bolt assembly which is anchored to the bolt assembly for reciprocating motion therewith and projects outwardly through a sidewall slot in the receiver for reciprocating motion with the bolt assembly. To releasably lock the bolt assembly in its rearward position the bolt pin is rearwardly moved into the locking apparatus slot, and a latch portion of the locking apparatus is moved to block forward exit of the pin from the locking apparatus slot.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/052,755 filed on May 13, 2008 and entitled “Machine Gun Bolt Pin Locking Apparatus”, such provisional application being hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to machine gun apparatus and, in a representatively illustrated embodiment thereof, more particularly relates to a specially designed machine gun bolt pin locking apparatus. 
     In a conventional machine gun such as, for example, a .50 caliber machine gun, the body or receiver portion of the gun has disposed therein a bolt assembly which reciprocates forwardly and rearwardly as the gun is fired. The bolt assembly is strongly spring-biased in a forward direction, and carries a bolt pin member which projects outwardly through a horizontally elongated slot on a vertical side wall of the receiver for reciprocation with the bolt assembly. To enable the manual rearward movement of the bolt assembly, an external charging handle is typically secured to the outwardly projecting bolt pin. 
     Access to the interior of the receiver, and the bolt assembly therein, is provided by means of an access door carried by the receiver. The interior of the receiver is typically accessed through this door to clear ammunition jams, and, during an idle period of the gun after a firing sequence, to hold the bolt assembly (and the next-to-be fired round which it caries) rearwardly away from the still-hot barrel to prevent an undesirable “cook-off” firing of the next round by the heat of the barrel. 
     As is conventionally practiced, this holding of the bolt assembly in such rearward orientation away from the barrel, is accomplished by opening the receiver access door, pulling the bolt assembly rearwardly using the exterior charging handle secured thereto, and then pivotally moving a round extractor structure within the interior of the receiver until the round extractor is braced against the receiver interior in a manner preventing the spring-biased bolt assembly from snapping back to its original forwardly disposed position within the receiver. 
     Unfortunately, injury to operators&#39; hands and fingers within the receiver interior is not an uncommon occurrence due to slippage of the repositioned round extractor structure which permits he rearwardly held bolt assembly to rapidly and very strongly snap back to its forwardly disposed position within the interior of the receiver. For this reason it can readily be seen that a need exists for a safer and more reliable technique for holding the spring-loaded bolt assembly in a rearwardly disposed orientation within the interior of the receiver. It is to this need that the present invention is directed. 
     SUMMARY OF THE INVENTION 
     In carrying out principles of the present invention, in accordance with a representatively illustrated embodiment thereof, a specially designed bolt pin locking apparatus is provided for use with a machine gun having a receiver from which an outer end portion of an internal bolt pin outwardly projects through a horizontally elongated slot, representatively disposed in a side wall of the receiver opposite from the side wall from which the charging handle outwardly projects, the bolt pin being movable between forward and rearward positions relative to the receiver and being spring-biased toward the forward position. 
     From a broad perspective, the bolt pin locking apparatus comprises a body adapted to be externally mounted on the receiver rearwardly of an outer end portion of the bolt pin in its forward position and having a slot formed therein, the slot having front and rear end portions and being configured to permit movement of the outer bolt pin end portion rearwardly therethrough to its rearward position. A latch member carried by the body for movement relative thereto, in a direction transverse to the direction of movement of the outer bolt pin end portion to its rearward position, between a locking position in which the latch member blocks the front end portion of the slot, to thereby be forcibly engaged by the outer bolt pin end portion and captively retain the outer bolt pin end portion in the slot, and an unlocking position in which the latch member unblocks the slot and permits the outer bolt pin end portion to be spring-returned to its forward position. 
     According to other aspects of the invention, a biasing spring structure may be carried by the bolt pin locking apparatus body and resiliently bias the latch member toward its unlocking position, and the latch member may have a rear side surface portion with an arcuate notch formed therein and positioned to be aligned with the slot when the latch member is in its locking position. 
     Further, the body may have an internal passage for receiving and captively retaining the latch member for movement relative to the body into and out of the slot, the internal passage transversely intersecting the slot. The latch member is illustratively strip-shaped and is carried by the body for longitudinal movement within the internal passage, the internal passage extending on opposite sides of the slot, with one portion of the internal passage receiving an end portion of the latch member only when the latch member is in its locking position. 
     The latch member may have a transversely projecting portion captively retaining a portion of the latch member within the internal passage. A biasing spring structure may be disposed within the internal portion, with the biasing spring structure bearing on the transversely projecting portion of the latch member and resiliently urging the latch member toward its unlocking position. Illustratively, the body may have a generally plate-shaped base portion in which a groove is formed, and a cover plate removably secured to the base portion over the groove, the internal passage being defined by the groove and a side surface portion of the cover plate, with the slot extending through the base portion and the cover plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinally foreshortened, partially cut away perspective view of a representative machine gun upon which is operatively mounted an external bolt pin locking assembly embodying principles of the present invention, the bolt pin being in its forward orientation, and the locking assembly being in its unlocked position; 
         FIG. 2  is a view similar to that in  FIG. 1 , but with the machine bolt pin being releasably held in its rearward orientation by the locking assembly in its locked position; 
         FIG. 3  is an enlarged scale perspective view of a rear end portion of the machine gun with the bolt pin locking assembly in its unlocked position; 
         FIG. 4  is an enlarged perspective view of the bolt pin locking apparatus removed from the machine gun and being in its unlocked position; 
         FIG. 5  is an exploded perspective view of the bolt pin locking apparatus without internal biasing spring portions thereof; 
         FIG. 6  is an interior side view of the bolt pin locking apparatus in its unlocked position and with its cover plate removed; and 
         FIG. 7  is a view similar to that in  FIG. 6  but with the bolt pin locking apparatus being in its locked position. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrated in  FIGS. 1-3  is a machine gun  10  which is illustratively a .50 caliber machine gun, but could alternatively be a different type of machine gun having an external bolt pin  12 . The representatively illustrated bolt pin  12  extends outwardly from a front-to-rear extending slot  14  formed in a left side wall  16  of the body or receiver portion  18  of the machine gun  10 . During firing of the machine gun  10 , the bolt pin  12  reciprocates forwardly and rearwardly in the slot  14 . Disposed within the interior of the receiver  18  is a bolt assembly  19  which is secured to the bolt pin  12  for forward and rearward movement therewith relative to the receiver  18 . 
     Receiver  18  has a front end  20  from which a barrel  22  forwardly extends, a rear end  23 , and a right side wall  24  from which a charging handle  26  outwardly extends. The charging handle  26  is secured to a second bolt pin  12   a  that is also anchored to the bolt assembly  19  and extends outwardly through a horizontally elongated slot (not visible in the drawings) formed in the right side wall  24  of the receiver  18 . By rearwardly pulling the charging handle  26  the bolt pin  12  may be pulled rearwardly, against the forward force F of a strong spring (not visible) within the receiver  18 , from the forward position of the bolt pin  12  shown in  FIGS. 1 and 3  to the rearward position of the bolt pin  12  shown in  FIG. 2 . This rearward movement of the charging handle  26  is used to cock the machine gun  10 . 
     Access to the interior of the receiver  18 , and the bolt assembly  19  therein, is provided by means of an access door  28  mounted on the top side  30  of the receiver  18  for pivotal opening and closing movement relative to the receiver  18  about a forwardly disposed axis  32  on the receiver  18  as indicated by the dashed, double ended arrow  34  in  FIGS. 1 and 2 . The purpose of such access is typically twofold—(1) to clear ammunition jams, and (2) during an idle period of the gun after a firing sequence, to hold the bolt assembly (and the next-to-be fired round which it carries) rearwardly from the still-hot barrel  22  to prevent an undesirable “cook-off” firing of the next round by the heat of the barrel  22 . 
     As is conventionally practiced, this holding of the bolt assembly  19  in such rearward orientation away from the barrel  22 , for either of the two noted receiver interior access purposes, is accomplished by opening the access door  28 , pulling the charging handle  26  rearwardly (thus moving both the bolt pin  12  and the bolt assembly  19  rearwardly), and then pivotally moving a round extractor structure (not visible) within the interior of the receiver  18  until the round extractor is braced against the receiver interior in a manner preventing the spring-biased bolt assembly  19  from snapping back to its original forwardly disposed position within the receiver  18 . 
     Unfortunately, injury to operators&#39; hands and fingers within the receiver interior is not an uncommon occurrence due to slippage of the repositioned round extractor structure which permits the rearwardly held bolt assembly  19  to rapidly and very strongly snap back to its forwardly disposed position within the interior of the receiver  18 . For this reason it can readily be seen that it would be desirable to provide a safer and more reliable technique for holding the spring-loaded bolt assembly  19  in a rearwardly disposed orientation within the interior of the receiver  18 . To provide this desirable safety improvement, the present invention utilizes a specially designed bolt pin locking assembly  40  which is removably secured to the left side wall  16  of the receiver  18  adjacent the rear receiver end  23 . 
     With reference now to  FIGS. 4-7 , the bolt pin locking assembly  40  is illustratively of a suitable metal construction and comprises a body formed from vertically elongated rectangular base plate and cover plate portions  42  and  44 , a vertically elongated, generally strip-shaped bolt pin retention latch member  46 , a pair of compression spring members  48 , and a pair of spring stop pins  49 . 
     Base plate  42  (see  FIGS. 5-7 ) has outer and inner side surfaces  50  and  52 , top and bottom end edge surfaces  54  and  56 , and front and rear side edge surfaces  58  and  60 . A slot  62  extends rearwardly through the front edge surface  58  at a vertically intermediate location thereon and has a curved rear end  64 . A first recess  66  is formed in the inner side surface  52  of the base plate  42  and extends upwardly from the top side surface of the slot  62 . A somewhat wider second recess  68  is also formed in the inner side surface  52  of the base plate  42 , the second recess  68  being horizontally aligned with the first recess  66  and vertically extending outwardly through the bottom side surface of the slot  62  and the bottom end surface  56  of the base plate  42 . The top end of the second recess  68  is narrowed by inwardly projecting wall portions  70  of the base plate  42 , and the bottom end of the second recess  68  is narrowed by inwardly projecting wall portions  72  of the base plate  42 . The stop pins  49  are retained in suitable mounting holes (not visible) formed in the base plate  42  just below the inwardly projecting top wall portions  70 . 
     Cover plate  44  has a slot  74  horizontally extending inwardly from its front edge  76  and having a configuration identical to that of the base plate slot  62 . As best illustrated in  FIGS. 4 and 5 , the cover plate  44  is securable to the inner side  52  of the base plate  42 , illustratively by means of rivets  78  insertable into alignable opening sets  80 , 82  respectively extending through the cover plate  44  and the base plate  42 . 
     With continuing reference to  FIGS. 4-7 , the latch member  46  has a vertically elongated, generally rectangular strip-shaped body  83  having an upper end surface  84 , a transversely outwardly bent lower end portion  86 , front and rear side edge surfaces  88  and  90 , a pair of vertically aligned projections  92 , 94  respectively formed on vertically intermediate portions of the side edge surfaces  88  and  90 , and an arcuate notch  96  formed on the rear side edge surface  90  and disposed between the rear projection  94  and the upper end surface  84 . 
     To assemble the bolt pin locking assembly  40 , an upper longitudinal portion of the latch member  46  is inserted into the recess  68  in the inner side surface  52  of the base plate  42  in a manner such that the latch member side edge projections  92 , 94  are disposed within the recess  68  and downwardly abut the lower recess projections  72  as shown in  FIG. 6 . Next, the compression spring members  48  are placed in the side surface recess  68  so that the spring members  48  are on opposite front and rear sides of the latch member body  83  with the upper ends of the spring members  48  abutting the previously installed stop pins  49  and the lower ends of the spring members  48  abutting the flat upper sides of the latch member side edge projections  92 , 94 . With the spring members  48  installed, and the latch member  46  in the position shown in  FIG. 6 , the spring members  48  are in their relaxed positions, and the upper end surface  84  of the installed latch member  46  is essentially flush with the bottom side of the slot  62 . 
     As can be seen in  FIG. 6 , the bottom recess projections  72 , the pins  49 , and the body edge projections  92 , 94  prevent vertical removal of the installed latch member  46  from the recess  68 . The installed latch member  46  may be upwardly moved from its  FIG. 6  unlocking position, in which the compression spring members  48  are in relaxed orientations, to its  FIG. 7  locking position in which the spring members  48  are compressed, an upper end portion of the latch member body  83  enters the upper recess  66 , and the arcuate notch  96  of the latch member body  83  is disposed in a rearwardly facing orientation within the base plate slot  62 . As can also be seen in  FIG. 7 , with the latch member  46  in this locking orientation the spring members  48  resiliently bias the latch member  46  downwardly toward its  FIG. 6  unlocking position. 
     Finally, as illustrated in  FIG. 4 , the cover plate  44  is secured to the side  52  of the base plate  42  using the rivets  78  which are extended through the previously described alignable opening sets  80  and  82  in the cover plate  44  and the base plate  42 . As can be seen in  FIG. 4 , this aligns the base plate and cover plate slots  62  and  74  to form therefrom a combined assembly slot structure  62 , 74 . The completed bolt pin locking assembly  40  is then externally mounted on a rear side portion of the machine gun receiver  18  (as shown in  FIGS. 1-3 ) using screws (not shown) extended through screw holes  98  formed in the base and cover plates  42 , 44  (see  FIGS. 4-7 ) and then threaded into underlying holes (not visible) formed in the receiver  18 . With the assembly  40  installed in this manner, the assembly slot  62 , 74  (see  FIGS. 1-3 ) outwardly overlies, and is aligned with, a rear end portion of the receiver bolt pin slot  14 . 
     When it is desired to hold the bolt assembly  19  in a rearwardly shifted orientation against the internal receiver spring force F, the charging handle  26  is pulled rearwardly to cause the bolt pin  12  to move rearwardly from its  FIG. 1  forward position toward a rearward position in a manner causing the bolt pin  12  to pass rearwardly through the locking assembly slot  62 , 74  to a position in which the bolt pin  12  is positioned just rearwardly of the upper end of the latch member  46  which, at this point, is held in its lowered, unlocking orientation by the compression spring members  48  (see  FIG. 6 ). With the bolt pin  12  held in its rearwardly shifted position the latch member  46  is moved upwardly to its  FIG. 2  locking orientation in which the latch member arcuate notch  96  (see  FIG. 7 ) is disposed in the assembly slot  62 , 74  just forwardly of the bolt pin  12 . The charging handle  26  is then released to permit the internal receiver spring force F to drive a front side portion of the bolt pin  12  into forcible engagement with the arcuate latch member notch  96  as depicted in phantom in  FIG. 7 . 
     This forcible engagement of the bolt pin  12  with the notch area  96  of the latch member body  83  prevents the downward force  100  of the compression spring members  48  from returning the latch member  46  from its  FIG. 7  locking position to its  FIG. 6  unlocking position. As can be seen in  FIG. 7 , the latch member in its locking position positively blocks the rearwardly shifted bolt pin  12  (and the bolt assembly  19 ) from returning to its receiver spring-biased forward position, thereby allowing safe access to the receiver interior, via the receiver access door  28 , with the bolt assembly  19  (via the positively blocked bolt pin  12 ) safely held in a rearwardly disposed orientation, and also securely holding the rearwardly shifted bolt assembly  19  (and the next-to-be-fired round which it carries) safely away from the hot gun barrel  22 . 
     When it is desired to return the rearwardly shifted bolt assembly  19  to its forward position, all that is necessary is to pull back on and then release the charging handle  26 . When the charging handle  26  is initially pulled back, to rearwardly remove the bolt pin  12  from the latch member notch  96 , the downward biasing force of the compression spring members  48  downwardly snaps the latch member  46  back to its  FIG. 6  unlocking position, as schematically indicated by the dashed arrow  100  in  FIG. 7 , thereby moving the latch member  46  out of its previous blocking relationship with the bolt pin  12 . The subsequent release of the charging handle  26  permits the internal receiver spring to drive the now released bolt assembly  19  back to its forward position. 
     As can be seen from the foregoing, the bolt pin locking assembly  40  of the present invention is of a simple, inexpensive and rugged construction, and may be easily and quickly retrofitted onto the illustrated .50 caliber machine gun  10  or onto other types of external bolt pin-type machine guns. Further, the assembly  40  operates in a simple, reliable manner which is seen to provide a desirable improvement over previously utilized techniques for releasably holding a machine gun bolt assembly in a rearwardly shifted orientation. While the bolt pin assembly  40  is representatively depicted as being externally secured to the left receiver side wall  16 , for operative receipt of the bolt pin  12 , it will be readily appreciated by those skilled in this particular art that the bolt pin assembly  40  could alternatively be externally secured to the right receiver side wall  24 , for operative receipt of the bolt pin  12   a  if desired, without departing from principles of the present invention. 
     The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.