Patent Publication Number: US-6910404-B2

Title: Gun bolt locking mechanism

Description:
This invention was made with Government support under contract DAAH23-00-C-A001 awarded by the U.S. Army Aviation &amp; Missile Command. The Government has certain rights in this invention. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a gun bolt locking mechanism. More particularly, the present invention relates to a device and method for locking a bolt to a bolt carrier during certain stages of the cycle of operation of a self-loading gun. It finds particular utility in a fully automatic gun and especially in a rotary, multi-barreled, machine gun. 
   The operation of self-loading, single-barreled guns is well known. Whether in semi-automatic or full automatic operation, the rate of fire is limited by the speed at which the gun can load, fire, and eject the spent cartridge of the ammunition being fired. Most of such weapons use the energy associated with the expanding gas or resulting recoil to operate the gun. Rotary machine guns are weapons that are designed to fire ammunition at an extremely high rate when compared to other types of weapons. A rotary machine gun includes a series of barrels that are mounted on a rotor assembly. The rotor assembly is externally driven, that is, power is applied to the rotor to rotate it with respect to a stationary gun housing to load, fire, and eject the spent casing as ammunition is fired in each barrel in rapid succession. As ammunition is fired in one barrel, a round is being loaded into another barrel, while a spent casing is extracted from yet another barrel. In this manner, the rotary machine gun achieves the high rate of fire. 
   Each round of ammunition is fired by igniting a primer contained within the cartridge case. There are two commonly used methods of igniting the primer. Some guns use electrical energy to ignite the primer, while other guns use mechanical force applied to the primer, normally by a firing pin. Accordingly, there are also two types of ammunition: electrically primed and percussion primed. Electrically primed ammunition must be fired with electrical energy and percussion primed ammunition must be fired with a mechanical impact. 
   Certain rotary machine guns manufactured by General Dynamics Armament and Technical Products are commonly used as part of the weapons systems on fighter aircraft. It has been discovered that under certain conditions, radiation generated by radar and communications equipment can ignite electrically primed ammunition. When these conditions occur, the uncontrolled ignition of the 20-mm shells creates a serious safety hazard. To eliminate this safety hazard, the aircraft should be able to switch from electrically-primed ammunition to percussion-primed ammunition with little or no modification to the gun. 
   In certain rotary machine guns having a reciprocating bolt associated with a reciprocating bolt carrier, a means is required to lock the gun bolt in an extended position relative to the bolt carrier during most of the gun cycle (cartridge extract, eject, rear dwell, cartridge feed, and cartridge ram), and to release the extended bolt during the rest of the gun cycle (bolt locking, firing, and unlocking). 
   With a rotary machine gun that only fires electrically-primed ammunition, the bolt locking mechanism can pass directly through the bolt body. For a firing mechanism that will work with both electric- and percussion-primed ammunition, however, the bolt locking mechanism cannot pass through the bolt body due to the need for a centrally-located firing pin and its spring mechanism. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a device and method for locking a bolt to a bolt carrier. While not limited to rotary, multiple-barreled machine guns, the preferred embodiment allows such a gun to fire both electric- or percussion-primed ammunition. 
   In accordance with one aspect, the present invention is directed to a carrier assembly for a gun. The assembly comprises a gun bolt carrier disposed to reciprocate axially with respect to the central axis of the gun, and a gun bolt disposed to reciprocate axially and rotate within the carrier. The gun bolt has a locking groove therein. The assembly also comprises a bolt locking mechanism extending through a portion of the bolt carrier to selectively engage the locking groove and thereby prevent the bolt from moving with respect to the carrier. The assembly further comprises a generally axial groove in a non-reciprocating portion of the gun that engages and selectively rotates the rotatable bolt locking mechanism to selectively lock the bolt to the carrier. 
   In accordance with another aspect, the present invention is directed to a multi-barreled machine gun having an externally powered rotor including a carrier assembly that reciprocates along the longitudinal axis of the rotor. The carrier assembly includes a bolt carrier having a gun bolt reciprocally mounted therein. The gun bolt includes a locking groove. The carrier assembly also includes a bolt locking mechanism for selectively locking the bolt to the carrier such that the machine gun is capable of firing both electric and percussion primed ammunition. The bolt locking mechanism comprises a selectively rotatable locking member extending through a portion of the bolt carrier to selectively engage the locking groove and thereby prevent the bolt from reciprocating axially within the carrier. The carrier assembly includes an axial groove in a non-reciprocating portion of the gun that engages and selectively rotates the selectively rotatable locking member to selectively lock the bolt to the carrier. 
   In accordance with another aspect, the present invention is directed to a method for selectively locking a gun bolt to a bolt carrier in a self-loading gun, including providing a gun bolt locking mechanism in the bolt carrier. The locking mechanism has a crank and crank pin at one end thereof. The crank pin engages a groove in a stationary portion of a gun. The groove is disposed to rotate the locking mechanism when the bolt carrier moves axially within the gun. The locking mechanism includes a bolt locking portion for engaging the bolt. The method also includes timing the rotation of the locking mechanism so that the bolt is locked to the bolt carrier during specific portions of the movement of the bolt. 
   In yet another aspect, the present invention is directed to the method recited above for a multi-barreled machine gun. 
   Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
   The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the present invention and together with the description, serve to explain the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top view of an embodiment of the invention, with the bolt in an extended position; 
       FIG. 2  is a front perspective view of the bolt carrier of  FIG. 1  (without the bolt); 
       FIG. 3  is a top view of the embodiment of  FIG. 1 , with the bolt in a retracted position; 
       FIG. 4  is a cross-sectional view of  FIG. 1 , with the bolt in an extended position and the bolt locking mechanism in a locked position; 
       FIG. 5  is a cross-sectional view of  FIG. 3 , with the bolt in a retracted position and the bolt locking mechanism in an unlocked position; 
       FIG. 6  is an exploded view of the embodiment of  FIG. 1 ; 
       FIG. 6A  is a cross-sectional view along lines  6 A— 6 A of the cocking pin of  FIG. 6 ; 
       FIG. 7A  is a front view of the bolt carrier and bolt locking mechanism of  FIG. 1  (without the bolt), with the bolt locking mechanism in a locked position; 
       FIG. 7B  is a front view of the bolt carrier and bolt locking mechanism of  FIG. 1  (without the bolt), with the bolt locking mechanism in an unlocked position; 
       FIG. 8  is a view of the gun bolt of the embodiment of  FIG. 1  illustrating the gun bolt&#39;s placement in a rotor of a rotary machine gun; 
       FIG. 9  is a bottom view of the bolt carrier of the embodiment of  FIG. 1 ; 
       FIG. 9A  is a bottom view of the embodiment of  FIG. 1 , with the bolt in an extended position and the bolt locking mechanism in a locked position; 
       FIG. 9B  is a bottom view of the embodiment of  FIG. 1 , with the bolt in a retracted position and the bolt locking mechanism in an unlocked position; 
       FIG. 10  is a view of the embodiment of  FIG. 1  illustrating the embodiment&#39;s placement in a rotor of a rotary machine gun; 
       FIG. 11  is a view of the embodiment of  FIG. 1  illustrating the gun bolt&#39;s placement in a rotor of a rotary machine gun; 
       FIG. 12  is a view of the embodiment of  FIG. 1  illustrating the gun bolt&#39;s placement in a rotor of a rotary machine gun; and 
       FIG. 13  is a view of the embodiment of  FIG. 1  illustrating the gun bolt&#39;s placement in a rotor of a rotary machine gun. 
   

   DESCRIPTION OF THE EMBODIMENTS 
   Reference will now be made in detail to embodiments of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
   In accordance with the invention there is provided a carrier assembly for a gun. The carrier assembly comprises a gun bolt carrier disposed to reciprocate axially with respect to the central axis of the gun, and a gun bolt disposed to reciprocate axially within the carrier. 
   As here embodied, and depicted in  FIG. 1 , the carrier assembly includes a bolt carrier  1  which houses a gun bolt  10 . As depicted in  FIG. 2 , the bolt carrier  1  includes a cylindrical opening  2  that is oriented along the central longitudinal axis A—A of the carrier  1 . The gun bolt  10  is mounted within the opening  2  in the bolt carrier  1  and reciprocates and rotates along the central axis A—A of the carrier  1  from an extended position shown in  FIG. 1  to a retracted position as shown in FIG.  3 . This embodiment is a multi-barreled, fully automatic machine gun. In such an embodiment the carrier  1  reciprocates parallel (or nearly so) to the central axis of the gun as the carrier  1  is rotated within a fixed housing (not shown) having interior cam surfaces (not shown) that interface with the carrier  1  and cause the reciprocating action of the carrier. This is the conventional manner of operation such a gun, and such operation is disclosed in U.S. Pat. No. 3,595,128 to Hoyt, Jr. which is incorporated by reference herein. The present invention, however, is not limited to this embodiment. The carrier assembly of the present invention could be a bolt assembly in a rifle or pistol that reciprocates by any means, such as by recoil, blowback, gas operation, or by manual manipulation of the carrier assembly. 
   As here embodied, and shown in  FIGS. 1 and 2 , the carrier  1  includes a central cam shaft bore  3  for receiving a cam shaft  20  that is surrounded by a cam roller  22 . The cam roller  22  engages the camming surfaces (not shown) in the surrounding housing (not shown) to reciprocate the carrier assembly parallel (or nearly so) to the central axis of the gun. To facilitate assembly, the cam shaft  20  can be inserted into the bore  3  along the bore axis, and when the cam shaft is appropriately located in the bore  3  it is detachably affixed to the carrier  1  such that it cannot move axially within the bore  3 . As shown in  FIG. 6 , in this embodiment the cam shaft  20  is allowed to rotate because, at the extremity of the cam shaft  20 , there is a camming surface  21  that engages a camming slot  18  in the bolt  10 . When the bolt  10  is not locked to the carrier  1 , movement of the carrier axially within the gun rotates the bolt  10  by the action of the camming surface  21  on the camming slot  18 . The amount of axial movement of the bolt  10  within the carrier  1  is determined by the length of the camming slot  18  and the angle of the camming slot  18  to the central axis A—A of the carrier  1  and bolt  10 . The amount of rotation of the bolt  10  within the carrier  1  is determined by the length of the camming surface  21  and the radial extent of the camming slot  18 . The bolt  10  is rotated in order to engage and disengage the locking lugs  14  on the face  12  of the bolt  10  from the locking lugs  102  (see  FIG. 10 ) in the barrel of the gun. Thus, the angle of bolt rotation is determined by the amount of rotation needed to lock and unlock the bolt from the barrel or chamber of the gun. 
   In accordance with the invention, the bolt in the carrier assembly includes a locking groove therein. As here embodied, and most clearly depicted in  FIGS. 4 and 5  the bolt  10  includes a locking groove  19  in the exterior surface of the bolt  10  that is transverse to the longitudinal axis B—B of the bolt  10 . While the embodiment depicted has a single locking groove in the bolt, more that one such groove can be used. As will be apparent from the disclosure below, the locking groove(s) in the bolt are to interface with components that lock the bolt to the bolt carrier. 
   In accordance with the invention the carrier assembly further includes a bolt locking mechanism extending through a portion of the bolt carrier to selectively engage the locking groove and thereby prevent the bolt from reciprocating axially within the carrier. Preferably, the bolt locking mechanism comprises an elongated shaft having a bolt passage groove therein, the bolt passage groove having a shape that allows the bolt to pass through the bolt passage groove. 
   As here embodied, and shown in  FIG. 6 , the carrier assembly includes a locking shaft  50 , that operates the bolt locking mechanism, with the locking shaft  50  having a bolt passage groove  54  therein. The locking shaft  50  further includes a shaft body  52 , a crank  56  and a crank pin  58 . As will be disclosed below, the crank  56  and the crank pin  58  operate with other portions of the gun to selectively rotate the locking shaft  50 . As shown in  FIG. 6 , the preferred embodiment of the invention has a bolt  10  that has a cylindrical outer surface, except for the face of the bolt having the locking lugs  12 . The cylindrical portion of the bolt  10  fits within the axial bore  2  of the carrier  1 , as depicted in  FIGS. 4 and 5 . In such an embodiment, the bolt passage groove  54  of the locking shaft  50  is semi-circular with a radius substantially equal to the radius of the cylindrical bolt. As here embodied, and depicted most clearly in  FIGS. 4 ,  5 ,  7 A and  7 B, rotation of the shaft  50  causes the bolt passage groove  54  to align with the sidewalls of the bore  2  in the configuration of  FIG. 7B  such that the bolt  10  may move axially (along axis A—A) within the bore  2 , or the shaft  50  can be rotated such that the shaft body  52  protrudes from the sidewall of the bore  2  to engage the locking groove  19  in the bolt  10 .  FIGS. 4 and 5  show the effect of the rotation of the locking shaft  50  on the locking of the bolt  10 . In  FIG. 4  the shaft body  52  is engaged with the locking groove  19  such that the bolt  10  cannot move axially within the bore  2  of the carrier  1 . In  FIG. 5  the shaft  50  has been rotated 45° such that the bolt passage groove  54  allows the bolt  10  to move axially within the bore  2  of the carrier  10 . 
   In accordance with the invention, the carrier assembly further includes a generally axial groove in a non-reciprocating portion of the gun that engages and selectively rotates the bolt locking mechanism to selectively lock the bolt to the carrier. By “generally axial” it is meant that the groove has its longitudinal axis generally aligned with the direction of linear movement of the carrier within the gun, but as will be disclosed in detail below, at least a portion of the groove is displaced with respect to the linear motion of the carrier to rotate the bolt locking mechanism. 
   As here embodied, and disclosed above, the locking shaft  50  further includes a crank  56  and a crank pin  58 . The crank pin  58  is offset from the axis of rotation of the locking shaft  50  such that movement of the crank pin  58  in a direction at an angle to the direction of the linear (reciprocating) motion of the carrier will rotate the locking shaft  50 .  FIG. 8  depicts an embodiment of the present invention where the non-reciprocating portion of the gun beneath the carrier  1  includes a groove  110  that is generally aligned with the direction of motion of the carrier  10 . The groove  110 , however, includes a displaced portion  112  that is displaced laterally with respect to the direction of reciprocating motion of the carrier  1 . In this embodiment, the crank pin  58  is placed within the groove  110  such that the reciprocating motion of the carrier along its linear axis causes the crank pin to move laterally with respect to the motion of the carrier such that the locking shaft  50  is rotated. The location of the displaced portion  112  of the groove  110  along the linear axis of the carrier  1  (and its direction of motion) is used to time the locking and unlocking of the bolt  10  to the carrier. What is meant by the “timing” of the locking and unlocking is the occurrence of locking and unlocking with respect to the cyclic operation of the gun. Because the location of the carrier along its linear path corresponds to certain operations of the gun, the location of the displaced portion  112  in the groove  110  along that linear direction causes the bolt to be locked and unlocked at specific positions during that cyclic operation. 
   The bolt  10  is locked in its extended position during the bolt cartridge extract, eject, rear dwell, cartridge feed, and cartridge ram stages of the gun cycle. It is only when the bolt locking mechanism  50  is rotated to release the bolt  10  that the bolt  10  can translate relative to the carrier  1  to its retracted position. The bolt  10  is released by the bolt locking mechanism  50  during the bolt locking, firing, and unlocking stages of the gun cycle. 
   Preferably, the bolt locking mechanism of the present invention includes a locking portion that engages the bolt carrier to prevent axial movement of the bolt locking mechanism. “Axial movement” of the bolt locking mechanism, means in a direction parallel to the length of the shaft body  52 . As here embodied, and depicted in  FIGS. 9A and B , the locking shaft  50  includes a flange  56 . As here embodied, the flange  56  comprises a radial segment of a circle. The flange  56  engages a portion of the bolt carrier  1  to prevent axial movement of the bolt locking shaft along its own axis. As here embodied, the bolt carrier  1  includes a circular groove  8  engaging the flange  56  to prevent axial movement of the locking shaft  50 . As depicted in  FIG. 10 , the groove  8  is preferably a radial segment of a circle. 
   An exemplary embodiment of a carrier assembly is illustrated in the exploded view of FIG.  6 . The bolt carrier  1  includes a forward opening  5  for a cocking pin  26  surrounded by an accompanying electrical insulator  28 . The carrier further includes a rear opening  4  for an insulator/bolt assembly pin  32  to extend therethrough. 
   The non-cylindrical portion of the gun bolt  10  preferably includes a bolt head  12  with locking lugs  14  and a flange extractor  16  for spent shell removal. The gun bolt  10  further includes a camming groove  18  for the cam shaft  20 , and a forward aperture  24  for the cocking pin  26 . A rear aperture  30  in the gun bolt  10  allows the insulator/bolt assembly pin  32  to slide therethrough. The bolt  10  also includes apertures  33  on opposing sides of a rear end of the bolt that accommodate flanges  42  of a tubular electrical insulator  40 . 
   The insulator  40  preferably includes a forward aperture  44  for the cocking pin  26  and a rear aperture  46  for the insulator/bolt assembly pin  32 . The insulator  40  also includes flanges  42 , and houses a firing pin  60 , a detent pin  70 , and a coil spring  80 . The detent pin  70  has a forward pin  72  that interacts with the cocking pin  26  and a rear spring guide  74  that interacts with the firing pin spring  80 . 
   Insulator/bolt assembly pin  32  is preferably a cylindrical shaft and may include identical grooves  34  an  36  on ends and a recess  38  along its length for receiving the end of the firing pin spring  80 . 
   The cocking pin  26  includes a detent  27  into which the forward pin  72  can be inserted. The cocking pin insulator  28  includes a rectangular slot  29  within which the cocking pin  26  can slide from its cocked position to its fired position. 
   The firing pin  60  preferably includes an aperture  64  at the rear, into which the cocking pin  26  is inserted. The cocking pin  26  is retained in the aperture  64  by the front pin  72  of detent pin  70 , that passes through the opening  61  in the rear of the firing pin  60  into the opening  27  of the cocking pin  26 . At the front of the firing pin  60  is a firing tip  66  for detonating a percussion primer. As disclosed above, the preferred embodiment is also capable of firing electrically primed ammunition. The firing pin is electrically isolated from the carrier assembly by the tubular insulator  40 , the insulator pin  32 , the insulator  28 , and a firing pin insulator  68  surrounding the tip  66  of the firing pin. As here embodied, and depicted in  FIG. 5A , the firing pin has a frusto-conical sleeve  68  affixed mechanically by means of a rim and groove arrangement adjacent the end  66  of the firing pin  60 . Thus an electrical current applied to the firing pin through the cocking pin  26  is not applied to the remainder of the bolt assembly. 
   In addition to providing electrical insulation to the firing pin  60 , the firing pin insulator can be made of an electrically insulating material, such as a polymer. The resilience of such a material on the surface of the firing pin reduces or prevents damage to the firing pin and firing pin recess in the bolt face caused by “dry firing” the gun. Moreover, the life of the firing pin and bolt face are extended by the ready and periodic replacement of such a firing pin insulator. 
   One method of assembling the components of the preferred embodiment includes placing the firing pin  60  into the rear opening of the tubular insulator  40 , and then the tubular insulator  40  is inserted into the bolt  10 . Lugs  42 , on opposing sides of the insulator  40  are inserted into apertures  33  on opposing sides of the bolt  10 , and the insulator is turned within the bolt so that the flanges  42  of the insulator  40  engage grooves (not shown) on the inner bolt wall to lock the insulator  40  within the bolt  10 . The insulator  40  is locked in the bolt  10  such that the forward apertures  24  and  44 , and rear apertures  30  and  46 , are substantially aligned. The insulator  28  is placed in the aperture  5 . 
   The bolt  10  is inserted into the bolt carrier  1  through bore  2 , so that the apertures  29 ,  24 , and  44 , the bore  3  and camming slot  18 , and the rear apertures,  4 ,  30 , and  46 , are substantially aligned. The cocking pin  26  is inserted through the apertures  29 ,  24 ,  44 , and  64  of the insulator, the bolt, the tubular insulator, and firing pin respectively. 
   Next, the detent pin  70  is inserted into the rear opening of the tubular insulator  40 , now housed within the bolt  10  and the carrier  1 , so that the forward pin  72  is inserted through the opening  61  in the back of the firing pin into the detent  27  in the cocking pin  26 . The coil spring  80  is then inserted into the rear opening of the tubular insulator  40  so that the rear spring guide  74  extends into the firing pin spring  80 . Next, the spring  80  is compressed and the insulator/bolt assembly pin  32  is inserted in the rear apertures  4 ,  30 ,  46 , of the carrier, the bolt, and the tubular insulator, respectively, and rotated such that the firing pin spring  80  is seated in the recess  38  of the pin  32 . 
   The cam shaft  20 , surrounded by the cam roller  22  is inserted into the carrier bore  3  and camming groove  18 , of the carrier and bolt, respectively. Preferably, the cam shaft  20  and the cam roller  22  are secured to the carrier  1  using a removable pin that simplifies assembly. 
   As can best be seen in  FIGS. 9A and 9B , after the carrier  1 , the bolt  10 , and the tubular insulator  40  have been assembled, the elongated shaft  52  of the bolt locking mechanism  50  is inserted into the bore  7  of the carrier  1 . In order to successfully insert the elongated shaft  52  of the bolt locking mechanism  50  into the bore  7  of the carrier  1 , the locking groove  19  of the gun bolt  10  must be substantially aligned with the bore  7  as depicted in FIG.  4 . The shaft  52  is inserted into the bore  7  such that the flange  60  of the pin  50  rests adjacent to the circular groove  8  on the carrier  1 . Once the shaft  52  is inserted all the way into the bore  7 , the bolt locking mechanism  50  is rotated so that the flange  60  of the bolt locking mechanism rotates into the circular groove portion  8  of the carrier  1 . This interaction of the circular groove portion  8  with the flange  60  retains the bolt locking mechanism  50  within the carrier  1  by restraining its movement in what is termed the axial direction, which, in this portion of the device, is along the axis of rotation of the shaft  52 . 
   A rotary machine gun typically includes multiple carrier assemblies that reciprocate along tracks in a non-reciprocating rotor. As can be seen in  FIGS. 10-14 , the rotor rotates the tracks, the cam path in the surrounding housing (not shown) for the cam roller  22  guides the carrier assemblies axially in a known manner between (1) the bolt cartridge extract, eject, rear dwell, and cartridge feed stages of the gun cycle (see  FIG. 11 , cartridge not shown), and (2) the cartridge ram, bolt locking, firing, and unlocking stages of the gun cycle (see  FIGS. 11-13 , cartridge not shown). 
   Firing in a particular carrier  1  occurs after the bolt head  12  rotates after insertion into the firing chamber  100  such that the locking lugs  14  of the bolt head  12  engage locking lugs  102  of the firing chamber  100  (see FIGS.  13 - 14 ). 
   As the carrier assembly is guided along the track  90 , the crank pin  58  extending from the bottom of the bolt locking mechanism  50  is guided toward the firing position by a generally axial groove that is illustrated as a cam groove  110 . Once the crank pin  58  of the bolt locking mechanism  50  reaches a laterally displaced portion of the cam groove  112  (see FIG.  10 ), movement of the crank pin  58  through the displaced portion  112  causes the bolt locking mechanism  50 , and particularly its elongated shaft  52 , to rotate such that the groove  54  in the shaft  52  faces inwardly, unlocking the bolt  10  from the carrier  1  and allowing translation of the bolt relative to the carrier. 
   Once the bolt  10  can translate relative to the carrier  1  and the breech bolt contacts the aft face of the barrel chamber, the cam shaft  20 , which is guiding the carrier assembly, is driven forward through the camming groove  18  in the bolt  10 , bringing the carrier  1  forward along the bolt  10 . When the carrier  1  slides forward along the bolt  10 , it pulls the insulator/bolt assembly pin  32  forward through groove  30  in the bolt  10 . Due to the curvature of the bolt grooves  18  and  30 , as the cam shaft  20  and insulator/bolt assembly pin  32  move forward through their respective grooves, the bolt  10  is forced to rotate relative to the carrier  1 . Due to proper placement of the displaced portion  112  of the groove  110 , this rotation occurs after the bolt face  12  has been inserted into the chamber  100 , and serves to rotate the bolt  10  so that the locking lugs  14  of the bolt face  12  engage the locking lugs  102  of the chamber  100  (see FIGS.  12  and  13 ). 
   Once the bolt face  12  has been locked in the chamber  100 , the cocking pin  26  is released from its cocked position. Because the firing pin  60  is biased in a forward direction by the coil spring  80 , it immediately slides forward in the rectangular slot  29  of the insulator  28  to its firing position (see FIG.  12 ). As the firing pin  60  moves to its firing position, it protrudes forward through a firing aperture  17  in the bolt face  12  (see  FIGS. 3 and 5 ) until the firing pin  60  detonates the percussion primer of the cartridge (not shown). If fire volts are applied through the cocking pin  26 , an electrical primer will detonate. 
   After the cartridge is fired, the carrier assembly is retracted toward its rear dwell position, ejecting the spent cartridge. The cam path for the cam shaft  20  and roller  22  guides them backward such that the cam shaft  20  and therefore the insulator/bolt assembly pin  32  slide through their respective grooves  18 ,  30 , in the bolt  10  until the bolt  10  is in an extended position relative to the carrier  1 . The shape of bolt grooves  18  and  30  causes the bolt head  12  to rotate so that locking lugs  14  of the bolt face  12  disengage the locking lugs  102  of the chamber  100 . As the carriage assembly slides back along the track, crank pin  58  of the bolt locking mechanism  50  is guided by the cam groove  110  such that when the crank pin  58  of the bolt locking mechanism  50  slides through the groove  110  of the cam groove, it rotates the bolt locking mechanism  50 , and particularly its shaft  52 , to lock the bolt in its extended position within the carrier  1  before the bolt has completely retracted from the barrel. 
   Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. For example, the present invention also contemplates other methods for guiding the bolt locking mechanism such as, for example, a rib that extends from the rotor along which the bolt locking mechanism slides. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.