Abstract:
A weapon system comprising a receiver, a barrel, a bolt, a barrel extension, a bolt carriage, and a toggle assembly. The barrel may have a longitudinal axis. The bolt may be spaced a distance from a rearward end of the barrel along the longitudinal axis of the barrel. The barrel extension may be attached to the bolt and connecting the barrel with the bolt. The barrel extension and bolt may be adapted to move linearly with respect to the receiver in a direction parallel to the longitudinal axis of the barrel. The bolt carriage may be movable relative to the bolt between an ammunition loading position and a firing position. The toggle assembly may be adapted to drive the bolt carriage between the loading position and the firing position in response to movement of the barrel extension and bolt relative to the receiver.

Description:
[0001]    This application is a continuation of, claims priority to, and incorporates by reference in its entirety, the following U.S. patent application Ser. No. 11/531,340, entitled “SELF-POWERED IMPULSE AVERAGING RECOIL OPERATED MACHINE GUN WITH A ROTARY LOCK BOLT DRIVEN BY BIMODAL CAMS” filed Sep. 13, 2006, which claims priority from U.S. provisional patent application Ser. No. 60/821,310, filed on Aug. 3, 2006, which is incorporated herein by reference in its entirety. 
     
    
     GOVERNMENT LICENSE RIGHTS 
       [0002]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of W15QKN-04-C-1093 awarded by the Department of Defense. 
     
    
     FIELD OF THE INVENTION 
       [0003]    Embodiments of the invention relate to an automatic weapon. More specifically, embodiments of the invention relate to a recoil operated automatic weapon with a rotary lock bolt. 
       BACKGROUND OF THE INVENTION 
       [0004]    Throughout history, military forces have been employed in offensive, defensive, and peace-keeping roles. In all roles, these military forces have required the use of weapons, and more particularly, firearm weapons. The present invention is directed to a machine gun with a rotary lock bolt driven by bimodal cams. 
       SUMMARY OF THE INVENTION 
       [0005]    One aspect of the present invention provides a weapon system comprising a receiver having at least one side plate with a bimodal cam way formed therein. The bimodal cam has an upper surface and a lower surface. A barrel extension is provided with at least a first end and at least one side plate with a cam way formed into the at least one side. A barrel is provided with a longitudinal axis and mounted to the barrel extension first end. A spring and buffer assembly is provided with a first end and a second end, wherein the first end is mounted to the barrel extension and the second end is mounted to the receiver. The mounted spring and buffer assembly are generally parallel to the barrel longitudinal axis. A bolt carriage is provided with a first end, a second end and at least one side plate, and a carriage cam way formed in the side plate. The weapon system further comprises a firing pin assembly fixed to the bolt carriage and having a bolt cam way. A rotary lock bolt having a first end, a second end, and a hollow pass-through is provided with the first end comprises a generally flat forward facing surface and a plurality of lugs radially arranged about the forward facing surface. The hollow pass-through extends through both first and second ends, and is shaped to telescopically receive the firing pin assembly. A bolt cam pin is adapted to be fixedly attached to the rotary lock bolt and simultaneously capable of sliding in and along the firing pin assembly bolt cam way. The relative movement of the bolt cam pin is relative movement along the longitudinal axis between the firing pin assembly and the rotary lock bolt causes the rotary lock bolt to rotate about the longitudinal axis due to the bolt cam pin riding in the bolt cam way. A toggle assembly having a toggle arm, a carriage cam way roller that rides in the carriage cam way, a barrel extension cam way roller that rides in the barrel extension cam way, and a receiver bimodal cam way roller to ride in the receiver bimodal cam way, the carriage cam way roller, barrel extension cam way roller and receiver cam way roller being collinear. The receiver roller rides on at least a portion of the bimodal cam way upper surface during a forward stroke of a firing cycle of the weapon system, and the receiver roller rides on at least a portion of the bimodal cam way lower surface during a rearward recoil stroke of a firing cycle of the weapon system. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0007]      FIG. 1A  is a preferred embodiment of the present invention shown in a perspective view from the right and rear of the invention. 
           [0008]      FIG. 1B  is a preferred embodiment of the present invention shown in a perspective view from the left and rear of the invention. 
           [0009]      FIG. 2  is a perspective view the receiver of the present invention. 
           [0010]      FIG. 3  illustrates a side view of the bimodal cam of the present invention. 
           [0011]      FIG. 4  depicts the operating group of the present invention. 
           [0012]      FIG. 5  is a perspective view of the barrel extension of the present invention. 
           [0013]      FIG. 6  is a perspective view of the rotary lock bolt assembly of the present invention. 
           [0014]      FIG. 7A  illustrates the rotary lock bolt of the present invention. 
           [0015]      FIG. 7B  shows the components used in conjunction with the rotary lock bolt of the present invention. 
           [0016]      FIG. 7C  depicts the round extractor of the present invention. 
           [0017]      FIG. 7D  is a side view of the round retainer of the present invention. 
           [0018]      FIG. 7E  illustrates the round ejector of the present invention. 
           [0019]      FIG. 7F  illustrates the round rammer of the present invention. 
           [0020]      FIG. 8A  illustrates the firing pin assembly of the present invention. 
           [0021]      FIG. 8B  shows the extraction buffer of the present invention. 
           [0022]      FIG. 8C  depicts the cam pin and cam pin retainer of the present invention. 
           [0023]      FIG. 8D  illustrates the firing pin of the present invention. 
           [0024]      FIG. 9A  depicts the rotary lock bolt assembly installed in the carriage. 
           [0025]      FIG. 9B  depicts the toggle assembly. 
           [0026]      FIG. 10A  is a top view of the operating group in the sear position. 
           [0027]      FIG. 10B  is a cross-sectional view of the present invention showing the position of the rollers in the sear position. 
           [0028]      FIG. 11A  is a top view of the operating group at the start of the firing cycle. 
           [0029]      FIG. 11B  is a cross-sectional view of the present invention showing the position of the rollers at the start of the firing cycle. 
           [0030]      FIG. 12A  is a top view of the operating group at a position of the firing cycle. 
           [0031]      FIG. 12B  is a cross-sectional view of the present invention showing the position of the rollers at a position of the firing cycle. 
           [0032]      FIG. 12C  is a cross-sectional view showing the bolt assembly stripping the round from the link with the rammer. 
           [0033]      FIG. 13A  is a top view of the operating group closing the chamber. 
           [0034]      FIG. 13B  is a cross-sectional view of the present invention showing the position of the rollers when the chamber is closed. 
           [0035]      FIG. 14A  is a top view of the operating group with the firing pin contacting the round. 
           [0036]      FIG. 14B  is a cross-sectional view showing the position of the rollers when the firing pin contacts the round. 
           [0037]      FIG. 15A  is a top view of the operating group at the start of recoil. 
           [0038]      FIG. 15B  is a cross-sectional view showing the position of rollers at the start of recoil. 
           [0039]      FIG. 16A  is a top view of the operating group ejecting a spent cartridge. 
           [0040]      FIG. 16B  is a cross-sectional view showing the position of the rollers when a spent cartridge is ejected. 
           [0041]      FIG. 16C  is a cross-sectional view showing the bolt assembly ejecting the round after firing. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]    The following description is intended to convey a thorough understanding of the invention by providing a number of specific embodiments and details involving an automatic weapon system  100 . It is understood, however, that the invention is not limited to these specific embodiments and details, which are exemplary only. It is further understood that one possessing ordinary skill in the art, in light of known systems and methods, would appreciate the use of the invention for its intended purposes and benefits in any number of alternative embodiments. Throughout the specification, the use of the terms “front” or “forward” refer to or toward the weapon system muzzle, and the terms “rear” or “rearward” refer to or toward the end of the weapon system  100  opposite the muzzle. 
         [0043]    Referring to  FIGS. 1A and 1B , a recoil operated gun system  100  is provided as an exemplary embodiment of the invention. The gun system  100  of the preferred embodiment comprises a receiver  200  and an operating group  300 . The gun system  100  comprises a feeder  102 , a cartridge guide  104 , an eject port  106 , and a trigger  108 . These components are generally known in the art. 
         [0044]    Referring now to  FIGS. 2 and 3 , the receiver  200  is adapted to at least partially house the internal operating group  300  (see  FIGS. 1A ,  1 B, and  4 ). The receiver  200  comprises a longitudinal generally U-shaped cradle  202  having a horizontal member and two parallel vertical sidewalls. The cradle  202  is a mounting platform for parallel left  204  and right  206  side plates. The two side plates  204 ,  206  are mounted on the vertical sidewalls of the cradle  202 . The cradle  202  further provides a mounting surface for a left cartridge guide mount  208  on the left side of the weapon  100 , and a sector gear  210 . The sector gear  210  interfaces with a pintle (not shown) to allow for precise control over the elevation or depression of the weapon system, such sector gears are generally known in the art. 
         [0045]    A bimodal cam way  212  is formed in each side plate  204 ,  206 . The two bimodal cam ways  212  are parallel to each other. Each side plate  204 ,  206  further comprise barrel extension rails  214  to guide the movement of the barrel extension  302  and toggles of the operating group  300 , these features are discussed in greater detail herein. The side plates  204 ,  206  also comprise mounting surfaces for a forward feeder mount  216  for mounting the ammunition feeder  102 . The left side plate  204  supports an active firing cam  220 , and the right side plate supports a right cartridge guide mount  218 . The active firing cam  220  is spring-loaded and biases the receiver rollers  382  to the upper surface of the bimodal cam way  212 . The left and right cartridge guide mounts  208 ,  218  provide a platform to mount the cartridge guide  104  (see  FIGS. 1A-1B ). Together, the side plates  204 ,  206  comprise mounting surfaces for left  222  and right  224  sear mounting plates for mounting a sear  226 , and mounting surfaces for mounting a rear side plate support  228 . Both the sear  226  and rear side plate support  228  are mounted transverse to the longitudinal axis of the cradle  202 . The right sear mounting plate  224  also supports the trigger  108  and trigger axial (not shown) which extends transversely across to the left  222  sear mounting through holes in plate. 
         [0046]    Referring to  FIG. 3 , the bimodal cam way  212  can generally be described as having an upper flat portion, a sloped portion, and a lower portion. An active cam gate  213  is attached to the receiver below the lower portion of the bimodal cam  212 . The cam gate  213  is spring loaded to be biased toward the top of the slots in the cam plates. The cam way  212  further has upper and lower surfaces. The function and use of the cam way  212  and its sections are discussed herein with respect to the weapon system operating cycle. 
         [0047]    With reference to  FIG. 4 , the operating group  300  comprises a barrel extension  302 , a barrel  304 , a chamber  305 , a bolt assembly  306 , a toggle assembly  308 , a detachable feed post  309 , an impulse averaging buffer assembly  400 , and a barrel lock  311 . Referring now to  FIG. 5 , the barrel extension  302  comprises two forward  312  (one not shown) and two rear  314  bearings to guide the barrel extension  302  along the length of the side plates  204 ,  206 , a forward barrel opening  316 , toggle track openings  318  on either side, barrel extension cam ways  320  on either side, carriage extractor slots  321 , an ejector post slot  322 , a carriage rail  323 , an eject window  324 , and a buffer mount  325 . The barrel  304  is preferably manufactured from Cr-Mo steel with a chromium-plated bore. However, the barrel  304  could be manufactured of other materials known in the art. The barrel  304  is also preferably 0.50 caliber and has a twist ratio of 1 turn per 9 inches of barrel length. The barrel may also be provided with a quick release feature, such as by rotating the barrel lock counter-clockwise until the lock clears the barrel then pull the barrel forward through the barrel extension opening. 
         [0048]    Referring now to  FIGS. 6-9 , the bolt assembly  306  comprises a carriage  326  with 4 bearings  328  and a cam way  330 , a rotary lock bolt  332  with a rammer  334 , rammer spring  335 , a round extractor  336 , a round retainer spring (not shown), an ejector  338  in the bolt  332 , and an ejector spring  340  and a fixed firing pin assembly  342 . 
         [0049]    Referring now to  FIGS. 7A-7F , the rotary lock bolt  332  has a generally cylindrical body with a face on a forward surface. The face of the bolt  332  closes the rear of the chamber  305  during firing of the weapon system  100 . A hollow cylinder runs the length of the bolt  332  to telescopically receive the firing pin assembly  342 . The cylinder extends the entire length of the bolt  332  to allow the firing pin  343  to extend forward of the bolt head  331  and into the chamber  305  to impact the primer during firing of the weapon system  100 . 
         [0050]    The round ejector  338  lies generally parallel with the axis of the barrel  304  and comprises a body  350 , a longitudinal finger  352 , and an ejector stop post  354 . The ejector finger  352  extends through and beyond the face of the bolt  332 . The ejector stop post  354  is formed at the base of the finger  352 , and the ejector body  350  is formed rearward of the post  354 . The body  350  is elongated and generally flat, it rides in a groove along the left circumferential side of the bolt  332 . The ejector spring  340  is circumferentially arranged about the finger  352  and is compressed between the bolt and the stop post  354 , biasing the finger  352  rearward keeping the finger clear of the forward surface of the bolt head  331 . 
         [0051]    The round rammer  334  is mounted in a groove formed in the top circumferential side of the bolt  332 . A pin (not shown) extends through an opening  333  in the bolt  332  and through the rammer pivot  356 . The rammer  334  is mounted to the bolt  332  so as to pivot about an axis that is perpendicular to the bolt axis and along a vertical plane. The rammer torsion spring  335  biases the rammer  334  in an up-pivoting position. 
         [0052]    The round extractor  336  comprises a claw-like edge  357 , a pivot  360 , and a hole  362 . The round extractor  336  is mounted in a groove formed in the face of the bolt  332 . A pin (not shown) extends through an opening  337  in the bolt  332  and through the extractor pivot  360 . The extractor  336  is mounted to the bolt  332  so as to pivot about an axis that is perpendicular to the bolt axis. A compression retainer spring (not shown) biases the extractor  336  so that it pivots in toward the bolt face  329 . The claw-like edge  357  facilitates gripping a cartridge  110  when it pivots into the bolt face  329 . The pivot  360  is inboard of the claw-like edge  357  thereby providing a moment about the pivot  360  to close the claw-like edge  357  against the round  110  if it pulls away from the bolt face  329 . The face of the claw-like edge  357  has an angled surface  359  thereby allowing the round extractor  336  to be forced open when a round  110  is pushed toward the bolt face  329 , allowing the round  110  into the bolt face  329 . 
         [0053]    With reference now to  FIGS. 8A-8D , the firing pin assembly  342  comprises a firing pin  343 , a bolt cam pin  344 , a cam pin retainer  346 , and an extraction buffer  348 . The firing pin  343  extends from a forward surface of a firing pin body  366 . The firing pin body  366  comprises a hollow cylinder with two helix bolt cams  368  in which the bolt cam pin  344  rides and a cylindrical rear opening  367 . The bolt cams  368  are openings in the circumferential surface of the firing pin body  366  with a width slightly wider than the circumference of the bolt cam pin  344 . The forward end of the cams  368  generally follow helical path generally 30° relative to a longitudinal axis of the firing pin body  366 . The rearward end of the cams  368 , however are generally parallel to the same longitudinal axis. The firing pin body  366  comprises torsion restraining lugs  370 . The firing pin body  366  further comprises threads at the rearward end of the opening  367  to threadedly secure the cam pin retainer  346 . 
         [0054]    The cam pin retainer  346  comprises a cylindrical body  349  with lug  351  attached at the rear. A cam pin retainer shaft  347  extends from a forward surface of the cam pin retainer body  349  to retain the cam pin  344  in the bolt cams  368  by extending into an opening in the circumferential side of the cam pin  344 . The cam pin  344  is free to slide and rotate about the cam pin retainer shaft  347 . The cam pin retainer  346  forward end is threadedly received within the firing pin rear opening  367  so that the shaft  347  extends into the firing pin body  366  and the cam pin  344  is free to slide through the twisting bolt cams  368 . An extraction buffer  348  is retained on the cam pin retainer body  349  between the firing pin body  366  and the lug  351 . 
         [0055]    Referring now to  FIGS. 4 and 9 , the forward end of the carriage  326  comprises a bolt opening  364  to telescopically receive both the firing pin  343  and the bolt  332 . The torsion restraining lugs  370  fit in recesses at the rear end of the carriage  326  to prevent the firing pin  343  from rotating about the axis of the bolt  332 . The bolt  332  is then inserted into the opening  364  and the cam pin  344  is inserted through the cam pin openings  333  and the bolt cams  368 . The cam pin retainer  346 , with the extraction buffer  348  already attached, is then inserted into a retainer opening  372  at the rear of the carriage  326  and threaded into the firing pin rear opening  367 . The firing pin  343  is now axially fixed to the carriage  326 . The carriage  326  holds the firing pin  343  and bolt  332  collinear. The bolt  332  is now able to slide along the length of the firing pin  343  and rotate about the firing pin  343 , following the bolt cams  368  through the cam pin  344 . The carriage  332  is inserted into the barrel extension  302  through the carriage extraction slots  321 . The barrel extension  302  now retains the firing pin  343 , bolt  332 , chamber  305 , and barrel  304  collinear. The bolt cam pin  344  rides in the bolt cams  368  thereby defining both the rotational and axial position of the bolt  332 . A bolt lug is restrained from rotation by a bolt side rail (not shown) in the barrel extension  302  thereby retaining the bolt  332  and bolt face  329  forward of the firing pin during the first half of the firing cycle. 
         [0056]    The toggle assembly  308  comprises left  374  and right  375  toggles, a toggle shaft  376 , a carriage roller  378 , barrel extension rollers  380 , a receiver roller  382 , and rear rollers  384 . The toggle shaft  376  connects the two toggles  374 ,  375 . A rear roller  384  is positioned between the shaft  376  and each toggle  374 ,  375  and allows the toggle assembly  308  to ride in the toggle track openings  318  on the barrel extension  302 . The left toggle  374  extends forward and connects to a barrel extension roller  380 . The right toggle  375  extends forward parallel to the left toggle  374 . The right toggle  375  is attached to a collinear stack of rollers, the carriage roller  378 , a barrel extension roller  380 , and the receiver roller  382 . The carriage roller  378  rides in the carriage cam way  330 , the barrel extension rollers  380  ride in the barrel extension cam ways  320 , and the receiver roller  382  rides in the receiver&#39;s bimodal cam way  212 . Because these rollers are collinear, the carriage cam way, the barrel extension cam way  320  and the bimodal cam way  212  will always share an intersecting point. These rollers and cams work together to adjust the position and speed of the carriage  326  relative to the barrel extension  302  as the barrel extension  302  moves through the receiver  200  during the operating cycle. An ejector bar  390  is attached to the side of and is collinear with and free to rotate about the toggle shaft  376 . The front of the ejector bar  390  is supported by a groove in the ejector  338  and the front of the ejector bar  390  rests on the ejector post  354  pushing the round ejector  338  forward. 
         [0057]    Embodiments of the recoil system are described in U.S. Pat. No. 6,343,536 which is incorporated herein by reference. 
         [0058]    With reference to  FIGS. 10A-17 , the cycle of the weapon system  100  will now be discussed in detail. With the weapon  100  in a neutral position [?], the operator first charges the weapon  100 , as is known in the art 
         [0059]    Referring to  FIGS. 10A-10B , with the weapon  100  is charged with the barrel extension  302  located at the rear of the receiver  200  where it is held back by a hook on the sear  226  (see  FIG. 11B ). The bolt carriage  326  is positioned to the rear of the barrel extension  302  and held in place by the rollers  378 ,  380 ,  382  located at the top of their respective cam ways  330 ,  320 ,  212 . The round ejector finger  352  extends forward of the bolt head  331  and is held in this position by the ejector stop post  354 . A cartridge  110  is in the strip position in the cartridge guide  104 . 
         [0060]    With reference to  FIG. 11 , the operator initiates the firing sequence by carefully aiming the weapon system  100  and pulling the trigger  108 . The trigger  108  moves the sear  226  out of the way, releasing the barrel extension  302 , allowing the buffer main spring  402  to push the barrel extension  302  forward. The receiver roller  382  moves along the upper portion of the bimodal cam way  212 . With the barrel extension  302  0.25 inches from the sear position, the rammer  334  engages the cartridge  110  and pushes it through a link (not shown). 
         [0061]    Referring now to  FIGS. 12A-12C , the barrel extension  302  continues forward, the receiver roller  382  enters the downward sloping portions of the bimodal cam way  212 , pushing the receiver roller  382 , barrel extension roller  380 , and carriage roller  378  through a downward changing slope. Moving through the changing slope, the barrel extension roller  380  begins to move downward and decelerate the barrel extension  302 . At the same time, the carriage roller  378  pushes on the carriage cam way  330  to increase the carriage  326  acceleration relative to that of the barrel extension  302 . With the barrel extension  302  2.57 inches from the sear position, the rammer  334  to begins to push the cartridge  110  into the barrel chamber  305 . At 3.1 inches from the sear position, the bolt assembly  306  and bolt carriage  326  have traveled farther than the ejector bar  390 . This relieves the ejector stop  354  of the ejector bar  390  and allows the ejector spring  340  to push the ejector  338  rearward, clearing the ejector from the bolt face  329 . 
         [0062]    With reference now to  FIGS. 13A and 13B , the barrel extension  302  continues forward with enough momentum to drive the ammunition feeder  102 , which indexes the next cartridge into position. Such feed systems are generally known in the art, such as, for example, that disclosed by U.S. Pat. No. 6,343,536, which is incorporated herein by reference. As the barrel extension  302  continues forward, the receiver roller  382  moves through the relieved portion of the bimodal cam way (see  FIG. 13B ). The carriage  326  is slowed down relative to the receiver and barrel extension and the receiver roller  382  is forced to the upper surface of the bimodal cam by the active cam gate  213 . With the barrel extension 7.2 inches from the sear position, the bolt head  331  closes the chamber  305  and its forward motion stops. As the chamber  305  closes, the forward motion of the ammunition round  110  is stopped by the barrel and it is forced into the round extractor  336 . The carriage  326  however continues forward relative to the bolt  332 . Moving forward, the carriage  326  pushes the firing pin forward, which cause the bolt cam pin  344  to move through the bolt cams  368  forcing the bolt  332  to rotate clockwise. 
         [0063]    Referring now to  FIGS. 14A and 14B , the barrel extension  302  continues forward, driving the receiver roller  382  farther through the bimodal cam  212 , accelerating the carriage  326 . The firing pin assembly  342  continues forward, rotating the bolt  332  until it locks with the chamber  305 . With the barrel extension 8.0 inches from the sear position, the carriage  326  drives the firing pin  343  into the cartridge primer, causing the propulsion train to ignite and push the bullet out of the barrel  304 . At this time, the barrel extension  302  forward movement is stopped and it is driven rearward from the impulse of the fired round. 
         [0064]    Referring now to  FIGS. 15A-16C , the unlocking of the bolt will now be explained. Due to the impulse of the fired round, the barrel extension  302  moves rearward, driving the receiver roller  382  into the lower surface of the bimodal cam  212 . The carriage  326  then accelerates rearward by the receiver roller  382  moving through the upward slope of the bimodal cam  212  (see  FIG. 16B ). At the same time, the barrel extension rollers  380  and carriage roller  378  move upward in their respective cam ways  330 ,  320 . As the carriage  326  moves rearward, the bolt  332  is initially still held in the chamber  305  as the cam pin  344  moves through the straight portion of the bolt cam  368 . When the carriage  326  proceeds farther rearward, the cam pin  344  enters the helical portion of the bolt cam  368  and the bolt  332  rotates counterclockwise and is unlocked from the chamber  305  and pulled rearward by the carriage  326 . 
         [0065]    With reference to  FIGS. 16A-16C , the barrel extension  302  continues rearward driving the rollers  378 ,  380 ,  382  upward and along their respective cam ways  330 ,  320 ,  212 . The forward claw-like edge  357  of the round extractor  336  grips the rim of the cartridge  110  and pulls the cartridge  110  out of the chamber  305 . The receiver roller now enters the upward sloped portion of the bimodal cam  212  and decelerates the rearward moving carriage  326 . The ejector stop post  354  then engages the ejector stop  354  (See  FIG. 16C ) causing the ejector finger  352  to extend forward of the bolt head  331 , impacting the back of the cartridge  110  near its circumferential edge, pushing the cartridge  110  off the bolt head  331  and out of the grip of the round extractor  336  and rotating the cartridge  110  laterally clear of the weapon through the eject port  106 . 
         [0066]    The barrel extension  302  continues rearward driving the receiver roller  382  into top portion of the bimodal cam  212  to sear the carriage  326 . The barrel extension  302  continues rearward until the buffer assembly  400  stops it. The barrel extension  302  will then sear up or continue forward to repeat the firing cycle, depending on the operating mode and the orientation of the trigger  108 . The sear position is illustrated in  FIGS. 10A and 10B . 
         [0067]    While the firing cycle has been described at 7 discrete points relating to  FIGS. 10A-16B , these 7 discrete positions have been described merely for illustrative purposes only. It should be understood that, in operation, the present invention&#39;s firing cycle comprises a smooth and continuous sequence of motion, taking the operating group  300  from sear position, to firing the round, and back to sear position. 
         [0068]    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. It is intended that the specification be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.