US3715954A

US3715954A - Firing mechanism for a multi purpose firearm

Info

Publication number: US3715954A
Application number: US00176417A
Authority: US
Inventors: E Rude
Original assignee: United States Department of the Army
Current assignee: United States Department of the Army
Priority date: 1971-08-31
Filing date: 1971-08-31
Publication date: 1973-02-13
Anticipated expiration: 1990-02-13

Abstract

A firearm having both point and area fire power comprises a rifle and grenade launcher mounted thereon. A firing mechanism in the rifle selectively adapts the firearm for semiautomatic fire, automatic fire at a reduced rate, three round bursts and grenade fire from a single trigger and comprises the trigger, a sear and a fire control mechanism operationally disposed therebetween in cooperation with a reciprocal firing pin to achieve the desired mode of fire as selected by a rotary selector. A counter is rotated by the firing pin to count the rounds in the three round burst and then disconnects the trigger from the sear for release thereof to hold the firing pin. In semiautomatic fire the selector rotates the counter to the position it is in after the second round of the three round burst and for automatic fire the automatic volley commences as with the semiautomatic fire and then continues until the trigger is released with an inertia wheel momentarily stopping the operation of the rifle after each round and then actuating the sear for release of the firing pin. For launcher fire, the selector disconnects the trigger from the sear and connects it to an arm linking the trigger to the launcher.

Description

United States Patent [1 1 Rude, Jr.

[ Feb. 13, 1973 [54] FIRING MECHANISM FOR A MULTI PURPOSE FIREARM [75] Inventor: Edward T. Rude, Jr., Columbia,

[73] Assignee: The United States of America as represented by the Secretary of the Army 22 Filed: Aug.3l, 1971 211 App1.No.: 176,417

[52] 11.8. C1. ..89/l27, 89/129, 89/131, 89/141, 89/142 [51] Int. Cl. ..F4Id 11/02 [58] Field of Search ..89/126, 127, 128, 129, 130, 89/131,141,142,145,l48

[56] References Cited UNITED STATES PATENTS 3,442,173 5/1969 Muller ..89/127 Primary Examiner-Stephen C. Bentley Attorney-Harry M. Saragovitz et a1.

[5 7 ABSTRACT A firearm having both point and area fire power comprises a rifle and grenade launcher mounted thereon. A firing mechanism in the rifle selectively adapts the firearm for semiautomatic fire, automatic fire at a reduced rate, three round bursts and grenade fire from a single trigger and comprises the trigger, a sear and a fire control mechanism operationally disposed therebetween in cooperation with a reciprocal firing pin to achieve the desired mode of fire as selected by a rotary selector. A counter is rotated by the firing pin to count the rounds in the three round burst and then disconnects the trigger from the sear for release thereof to hold the firing pin. In semiautomatic fire the selector rotates the counter to the position it is in after the second round of the three round burst and for automatic fire the automatic volley commences as with the semiautomatic fire and then continues until the trigger is released with an inertia wheel momentarily stopping the operation of the rifle after each round and then actuating the sear for release of the firing pin. For launcher fire, the selector disconnects the trigger from the sear and connects it to an arm linking the trigger to the launcher.

14 Claims, 10 Drawing Figures PATENTEI] FEB 1 3 I975 SHEET 10F 4 INVENTOR Edward THU d ll. 777 K M M 21376 ru s HY M f d 410/ [/r/ PATENTEDFEB13 197s SHEET 3 [IF 4 INVENTOR Edwuml T. Ru E19 11.

FIRING MECHANISM FOR A MULTI PURPOSE FIREARM BACKGROUND OF THE INVENTION a grenade'launc'he'rfThe rifle is selectively adaptable for various modes of operation including semiautomatic, automatic and bursts of a specific number of rounds and, to make the firearm as convenient to operate as possible, these modes of fire and the grenade launcher are effected by a single trigger.

The firing mechanisms which have been designed for such firearms have been overly complicated and are not as reliable as desired SUMMARY OF THE INVENTION It is therefore a particular object of this invention to provide for such a multi-purpose firearm a firing mechanism whereby the firearm can be selectively operated in semiautomatic, three round burst and automatic modes of point fire and in a semiautomatic mode of area fire.

It is a further object of this invention to provide such a firing mechanism which is simple in design and reliable in operation.

These objects are achieved by this invention which comprises a counter that is rotated by a reciprocating firing pin to count the rounds fired in the three round burst and then disconnects the trigger from the sear, which is thereby released to retain the firing pin, at the end of the burst. In semiautomatic operation, the operation selector rotates the counter to the position it is in after the second round is fired in the three round burst so that the firing pin is held by the sear after each round is fired. For automatic operation, the volley commences as with the semiautomatic operation and then continues until the trigger is released. To reduce a high cyclic rate of fire, an inertia wheel cooperates with the sear for momentarily stopping the operating cycle after each round is fired and then releasing the firing pin to fire the next round. For launcher operation, the selector disconnects the trigger from the sear and connects it to an arm linking the trigger to the launcher.

Further objects and advantages of the invention will become apparent from the following specification and the accompanying drawings which are for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational view of the multi-purpose firearm;

FIG. 2 is an enlarged elevational view of the firing mechanism with the right side of the housing removed to show the components with the selector rotated to a position for effecting a three round burst and the trigger located in its forward normal position;

FIG. 3 is an elevational view similar to FIG. 2 but shows only those components which cooperate in effecting the three round burst with the trigger pulled, the released firing pin in its position behind the operator which is in an elevated position;

FIG. 4 is a fragmentary view showing the actuator lock displaced by the counter to release the sear actuator and disconnect the sear from the trigger for rotation to its engaging position to end the three round burst;

FIG. 5 is a view similar to FIG. 4 but shows the selector rotated to a position for effecting semiautomatic fire and with the trigger in its pulled position;

FIG. 6 is an elevational view similar to FIGS. 2 and 3 but shows those components which cooperate to effect automatic fire at a reduced rate with the selector rotated to the automatic position, the lever released thereby to permit rotation of the inertia wheel into contact with the operator for actuation thereby, the trigger in its forward normal position and the firing pin seared in its cocked position;

FIG. 7 is a view similar to FIG. 6 but shows the firing pin seared after completing a firing cycle and the inertia wheel energized and located to where the sear cam is pivoted out of the way by the inertia wheel cam riser;

FIG. 8 is a fragmentary view similar to FIG. 7 but shows the sear can engaged by the cam riser during counterrotation of the inertia wheel and the sear pivoted thereby to its disengaging position;

FIG. 9 is a fragmentary view of the firing mechanism showing those components thereof which cooperate in effecting launcher discharge with the trigger pulled; and

FIG. 10 is a fragmentary view showing those components which cooperate when the safety is pulled to prevent operation of the firing mechanism.

DESCRIPTION OF A PREFERRED EMBODIMENT Shown in FIG. 1 is a multipurpose firearm 12 having both point and area fire power and comprising a rifle 14 and a grenade launcher 16 mounted to barrel 18 thereof. Operational control of firearm 12 is provided by a firing mechanism 20 which includes a firing pin 22 mounted in receiver 24 of rifle 14 for longitudinal nonrotating reciprocation, responsive to round discharge, between a forward firing position and a rearward recoil position. Firing pin 22 comprises a segmental recess 28, which forms a sear engaging lip 30 and a tang 32 extending rearwardly from the lip as shown in FIG. 2.

A trigger 36, including a forwardly and upwardly extending arm 40, is rotatingly mounted in housing 26 on a transverse pin 41. A sear 42 is mounted on a transverse pin 43 for rotational displacement thereon between a firing pin engaging position wherein firing pin 22 is releasably retained in a cocked position, as shown in FIG. 2, and a firing pin release position, as shown in FIG. 3. Sear 42 comprises an actuator arm 44 which extends rearwardly from an elbow 46, and a spring 47 is disposed to bias the sear for rotation in a clockwise direction to the engaging position wherein the actuator arm has contact with the surface 48 of a boss 50 on the inside of the left side wall of housing 26.

Operationally disposed between trigger 36 and sear 42 is a fire control mechanism 52 whereby, when trigger 36 is squeezed, either grenade launcher 16 is discharged or rifle 14 is fired semiautomatically, automatically at a reduced rate, or in a burst of three rounds at a rapid rate, as selected. Fire control mechanism 52 can best be understood through the illustration of the components which cooperate to effect the various modes of fire and the description of their functions.

THREE ROUND BURST FIRE In FIG. 2, selector 54 is shown rotated to a position which adapts firing mechanism for firing a three round burst each time that trigger 36 is pulled. In this position, the cooperating components of fire control mechanism 52 are free to move without any interference by the structural elements of selector 54. The firing cycle starts, as shown in FIG. 2, with trigger 36 in its normal forward position, and sear 42 is in its engaging position to thereby hold firing pin'22 in its cocked position. A sear actuator 56 is rotatingly mounted on a pin 58 which extends through trigger 36 spaced from pin 41 so as to be actuatable, as hereinafter described, against actuator arm 44 of sear 42 for displacement thereof to the release position. Referring to FIG. 3, sear actuator 56 is releasably held in a fixed position relative to trigger 36 by an actuator lock 60 which is rotatingly mounted on pin 41 and which comprises an arm 62 that extends forwardly for engagement with a notch 64 in the sear actuator. A spring 66 is operationally disposed between another arm 68 of actuator lock 60 and trigger 36 to resiliently hold arm 62 in notch 64 thereby forming a three part truss including the trigger, sear actuator 56 and the actuator lock. Thus,when trigger 36 is pulled it rotates about pin 41 to press sear actuator 56 downwardly against actuator arm 44 to thereby rotate sear 42 to its release position.

Rotatably mounted on a transverse shaft 69 is an operator 70 comprising a front section 71 which extends forwardly of the shaft and a rear section 72 which extends rearwardly therefrom. A spring 74 is disposed for biasing operator 70 for counterclockwise rotation to where front section 71 extends upwardly into the path of movement of firing pin 22 for contact by lip 30 and then tang 32 whereby the front section is depressed, when the firing pin goes forwardly past sear 42 to its firing position. Operator 70 is released to be based upwardly by spring 74 when firing pin 72 goes into its recoil position and recess 28 is in registry with the front section, as shown in FIG. 3. Pivotally mounted on rear section 72 is an actuating pawl 76 which, when operator 70 is released and is rotated in a counterclockwise direction by spring 74, acts against a ratchet wheel type of counter 78 which is rotated thereby one pitch against the bias of a spring 79. Counter 78 is provided with three ratchet type teeth 80, which are contactable by actuating pawl 76, and two notches 82 which are engageable by a holding pawl 84 to retain the counter against counterrotation. Holding pawl 84 is rotatably mounted on pin 41 and includes a catch 86 located rearwardly thereof and an arm 88 which extends oppositely therefrom. A spring 90 biases holding pawl 84 for clockwise rotation thereby pressing catch 86 towards counter 78 and arm 88 against sear actuator 56. Thus, when trigger 36 is in its normal position, as

' shown in FIG. 2, holding pawl 84 is rotated to where catch 86 is located away from counter 78 and, when the trigger is pulled, as shown in FIG. 3, the catch has engageable contact with notches 82.

Thus, with trigger 36 actuated and operator 70 is rotated by firing pin 22 to displace actuating pawl 76 downwardly against the first one of the teeth 80, counter 78 is rotated one pitch against the torque of holding pawl 84, as it is moved out of the first one of the notches 82 and snaps in the next to hold the counter against counterrotation. As firing pin 22 continues in counterrecoil to its striking position, to fire the second round of the three round burst, front section 71 of operator 70 is contacted by lip 30 to be driven downwardly thereby and then the above described action of operator 70, actuating pawl 76 and counter 78 is repeated for the next round. When the third round is fired, as shown in FIG. 4, operator 70 rotates counter 78 to where shoulder 92 thereon contacts actuator lock 60 for rotation thereby to disengage arm 62 thereof from notch 64 in sear actuator 56. Sear 42 is consequently freed to be rotated by spring 47 to engage firing pin 22 in its cocked position before the next round can be fired.

When trigger 36 is released, holding pawl 84 is rotated, by contact of arm 88 thereon with sear actuator 56, to move catch 86 away from counter 78 which is thereby freed for rotation by spring 79 back to its original position wherein an arm 94 on the counter has blocking contact with surface 96 of boss 98, and sear actuator 56 is pushed forwardly by trigger 36 through pin 58 to where notch 64 receives arm 62 of actuator lock 60 to reform the three part truss. Thus, firing mechanism 20 is reset to its initial position, shown in FIG. 2 and is ready to fire another three round burst when trigger 36 is actuated.

' SEMIAUTOM ATIC OPERATION For semiautomatic fire, selector 54 is rotated counterclockwise, as shown in FIG. 5, from its position for the three round bursts, thereby moving an extension 100 thereon against a shoulder 102 on counter 78 whereby the counter is rotated to the position it occupies after the second round of the three round burst described hereinbefore. Thus, when trigger 36 is actuated, fire control mechanism 52 counts the next round fired and then releases sear 42 as previously described. Releasing trigger 36 accomplishes all the actions previ ously described except that counter 78 is free to rotate only to the position it was in at the beginning of the semiautomatic fire with extension in contact with shoulder 102. Firing mechanism 20 is then ready to fire another round when trigger 36 is actuated.

Because of the high rate at which the operating mechanism (not shown) of rifle 14 functions, it is necessary when firing automatically to stop the operation momentarily after each firing cycle. This is accomplished with the aid of an inertia wheel 104 which is rotatingly mounted contiguous to sear 42 and operator 70. Referring to FIGS. 6-8, the components of fire control mechanism 52 which effect automatic fire at a reduced rate also comprise a lever 106 which is rotatably mounted on shaft 69 and includes a rear leg 110 that has contact with selector 54 and a front leg 1 12 that is contactable by a lug 1 14 extending from one side of inertia wheel 104. In addition, a lobe 116, comprising a radial surface 118, extends from the circumference of inertia wheel 104 and a cam riser 119 similar to lobe 116 in configuration extends from the circumference of a smaller diameter part 117 of the inertia wheel. An inertia wheel lock 120 is pivotally mounted contiguous to sear 42 and inertia wheel 104 biased by spring 121 into engagement with a circumferential recess 122 in the inertia wheel to block counterclockwise rotation thereof. A finger 123 on lock 120 is contactable with elbow 46 to thereby rotate the lock from recess 122 during displacement of scar 42 to the engaging position, as shown in FIG. 6. A coiled spring 126 biases inertia wheel 104 for rotation in a clockwise direction.

AUTOMATIC OPERATION When selector S4 is in the semiautomatic and three round burst position, an annular flange 128 thereon has contact with rear leg 1 of lever 106 whereby front leg 112 is displaced downwardly against lug 114 to rotate inertia wheel 104 counterclockwise to where lobe 116 is positioned away from contact by operator 70, and the inertia wheel is also blocked against counterclockwise rotation. For automatic fire, selector 54 is rotated counterclockwise from the semiautomatic position until chordal surface 130 on flange 128 is located under rear leg 110 of lever 106, as shown in FIG. 6. This permits rotation of lever 106, by the application of the energy of spring 126 thereagainst through lug 114 to front leg 112, to where surface 118 of lobe 116 is contactable by arm 127 of operator 70 when rotated downwardly. The rotation of selector 54 to the automatic position does not further change the functioning of the counting components of fire control mechanism 52 which are the same as for semiautomatic fire with the first round of each automatic volley being counted and actuator lock 60 then being disconnected from sear actuator 56 to thereby disconnect sear 42 from trigger 36 during the remainder of the volley.

Thus, when trigger 36 is actuated, sear 42 is disengaged from firing pin 22, as hereinbefore described for the semiautomatic fire, which is thereby free to be impelled forwardly to its firing position. Responsive to the discharge of the fired cartridge, firing pin 22 is driven rearwardly thereby releasing operator 70, when front section 71 thereof is in registry with recess 28, which is rotated rapidly about shaft 69 to rotate counter 78 one pitch whereby trigger 36 is released from sear 42 as hereinbefore described. This allows sear 42 to be rotated up into the path of firing pin 22 and move elbow 46 thereof against finger 123 of wheel lock 120 for pivotal disengagement from recess 122 in inertia wheel 104, as shown in FIG. 6. The pivotal displacement of operator 70, when released moves arm 127 thereof away from contact with surface 118 of lobe 116. Thus, thelast restraint is removed from inertia wheel 104 which consequently rotates several degrees clockwise until stopped by contact of lug 114 with front leg 112 of lever 106.

On the forward stroke of firing pin 22 to the firing position operator 70 is driven downwardly thereby against surface 118 of lobe 116 whereby inertia wheel 104 is spun in a counterclockwise direction. During this rotation, cam riser 119 contacts sear cam 132 which is pivotally mounted at elbow 46 of sear 42 so as to be displaced free thereof during the counterclockwise rotation of inertia wheel 104, as shown in FIG. 7. Inertia wheel 104 continues to rotate about 270 until all its energy is stored in spring 126 and during this time firing pin 22 is engaged by sear 42 and held cocked thereby. Inertia wheel 104 is then counterrotated under the bias of the stored energy in spring 126 in a clockwise direction. During this counterrotation, as shown in FIG. 8, cam riser 119 contacts sear cam 132, which is not free to move in this direction, so that the entire sear 42 is pivoted thereby to permit passage of the cam riser past the sear cam. This pivotal displacement of sear 42 releases firing pin 22 to fire the next round. Each time firing pin 22 contacts operator during displacement to the firing position inertia wheel 104 is spun around and then back to fire another round. When trigger 36 is released to its normal position, arm 40 thereon contacts leg 136 on operator 70 which is thereby prevented from springing back up into the path of firing pin 22. Thus, when firing pin 22 engages sear 42, and is held cocked thereby, and operator 70 is held inoperative, inertia wheel 104 is not rotated to disengage the sear from the firing pin so that firing stops. With the release of trigger 36, too, fire control mechanism 52 resets ready to fire another volley, as explained hereinbefore, under the description for semiautomatic operation.

LAUNCHER OPERATION Firing mechanism 20 is adapted to fire launcher 16 by rotating selector 54 clockwise several degrees from the three round burst position. As shown in FIG. 9, actuator lock 60 is elevated by the movement of shoulder 137 on selector 54 against tooth 138 on the actuator lock, shown in FIG. 10, away from engagement with notch 64 in sear actuator 56 so that it is not actuatable by trigger 36 when squeezed. This also aligns section 139 of selector 54 with a clearance 140 in launcher lever 142, which is pivotally mounted on pin 41 as shown in FIG. 9, to permit engagement of lever actuator 141, at 143, with the launcher lever so as to be actuatable by trigger 36. A linkage 144 is operatively connected with launcher lever 142, as shown in FIG. 9, thereby connecting firing mechanism 20 to grenade launcher 16, and is responsive to displacement by trigger 36 for discharge of the launcher.

Pivotally mounted in housing 26 forwardly of trigger 36, as shown in FIG. 10, is a safety 146 which comprises a manually actuated finger piece 148 and an arm 150 which is displaceable thereby against the underside of actuator arm 44 of scar 42 to prevent downward movement thereof.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. In a firearm comprising a combination rifle and grenade launcher, a universal firing mechanism therefor including a firing pin disposed for longitudinal reciprocation between a forward firing position and a recoil position, a first pin, a trigger rotatably mounted on said first pin for displacement between a forward normal position and a rearward actuating position, a sear disposed for engagement with said firing pin for releasable retention thereof in a cocked position, and a fire control mechanism comprising means cooperating with said firing pin, said trigger and said sear to provide selective operation of said rifle with respect to semiautomatic fire, automatic fire at a reduced rate and in a limited burst, and discharge of said launcher.

2. The invention as defined in claim 1 wherein said fire control mechanism means includes a counter disposed for actuation by said firing pin in response to selected limited burst operation to count the firing cycles of said firing mechanism, and means operationally disposed between said counter and trigger for disconnecting said trigger from said sear for release thereof to engage said firing pin in the cocked position when the burst is completed.

3. The invention as defined in claim 2 wherein said fire control mechanism includes a selector having means for displacing said counter to the position occupied thereby after the next to the last round in the burst is fired when said selector is located in a position to effect semiautomatic fire.

4. The invention as defined in claim 3 wherein said selector includes means cooperating with said fire control means responsive to rotation to a position to effect discharge of said launcher for disconnecting said sear from said trigger and connecting said trigger to said launcher for discharge thereof.

5. The invention as defined in claim 3 wherein said fire control mechanism includes inertia means, and said selector includes means having cooperation with said fire control mechanism means responsive to location at a position to effect automatic fire to initiate the automatic fire with the first round being counted by said counter as for semiautomatic fire and activating said inertia means for introducing a delay in the automatic fire after each round is fired.

6. The invention as defined in claim 3 wherein said fire control mechanism means includes a rotatingly mounted operator, a spring disposed for biasing said operator for rotation in one direction, means on said firing pin contactable with said operator during each operating cycle for rotating said operator in the opposite direction against the bias of said spring and subsequently releasing said operator for rotation by said spring, and an actuating pawl mounted on said operator for displacement against said counter for actuation thereof one pitch each operating cycle of said firing pin.

'7. The invention as defined in claim 6 wherein said operationally disposed means between said counter and said trigger comprises a second pin extending through said trigger spaced from said first pin, a sear actuator including a notch rotatably mounted on said second pin for displacement against said sear for actuation thereof to the release position in response to rotation of said trigger to the actuating position, an actuator lock rotatingly mounted on said first pin and including a first arm having engagement with said notch, and a spring disposed between said actuator lock and said first arm to resiliently hold said first arm in said notch thereby forming a three part truss to rigidly position said sear actuator relative to said trigger.

8. The invention as defined in claim 7 whereby said operationally disposed means between said counter and said trigger includes a shoulder on said counter disposed for actuation against said actuator lock when the last round in the burst is fired to rotate said actuator lock for displacement ofsaid first arm from said notch to break the rigid relationship of said sear actuator with said trigger and thereby permit release of said sear to the release position.

9. The invention as defined in claim 8 wherein said counter includes a plurality of teeth equal to the number of rounds to be fired in the burst formed around the circumference thereof, said teeth being operationally disposed for successive contact by said actuating pawl thereby rotating said counter one pitch each operating cycle of said firing pin.

10. The invention as defined in claim 9 wherein said fire control mechanism means is adapted by structure of said selector, when in the position to effect automatic fire, for said pawl to contact the last one of said teeth at the initiation of the automatic volley and then idle relative thereto during the remainder of the volley.

l 1. The invention as defined in claim 10 wherein said firing pin structure is of stepped configuration, a lip formed by said stepped configuration, and a tang extending rearwardly from said lip, said lip being engageable by said sear when in the engaging position for releasably retaining said firing pin in the cocked position, and said operator comprises a front arm having engagement with said lip during displacement of said firing pin from the recoil to the cocked position to thereby actuate said operator against the bias of said cooperating spring, and said front arm having contact with said tang in response to the subsequent displacement of said firing pin between the cocked and striking positions to retain said operator against rotation, and said front arm having registry with said recess during travel of said firing pin from the cocked to the recoil position to release said operator by said spring.

12. The invention as defined in claim 11 and including a plurality of notches formed around the circumference of said counter, a holding pawl rotatingly engageable with said'notches to prevent counter rotation of said counter after being rotated by said actuating pawl, and including an arm having contact with said sear actuator to effect rotation of said holding pawl out of engagement with said notches when said trigger is released to the normal position thereof at the end of a burst. 1

13. The invention as defined in claim 12 wherein said inertia means comprises an inertia wheel, a lobe comprising a radial surface extending from the circumference of said inertia wheel, a lug extending from one side thereof, a circumferential cam riser and a spring biasing said inertia wheel for rotation in one direction, said radial surface being contactable by said front arm of said operator for transferring rotation thereof when energized by said firing pin to said inertial wheel for rotation thereof until the energy transferred thereto is absorbed by said spring, and wherein said sear is provided with a scar cam pivotally mounted thereon in the path of said cam riser during rotation of said inertia wheel, said sear cam being pivotally disposed to permit passage of said cam riser thereby during rotation of said inertia wheel under the influence of said spring thereby transferring the rotation of said inertia wheel to said sear for displacement thereof to the disengaged position.

14. The invention as defined in claim 13 and including a rotatable lever having a front leg having contact with said lug on said inertia wheel and a rear leg having contact with said selector to hold said inertia wheel tioned for automatic tire to permit rotation of said inertia wheel by said spring to another position wherein said radial surface has contact with said operator for transferring rotation thereof to said inertia wheel.

Claims

7. The invention as defined in claim 6 wherein said operationally disposed means between said counter and said trigger comprises a second pin extending through said trigger spaced from said first pin, a sear actuator including a notch rotatably mounted on said second pin for displAcement against said sear for actuation thereof to the release position in response to rotation of said trigger to the actuating position, an actuator lock rotatingly mounted on said first pin and including a first arm having engagement with said notch, and a spring disposed between said actuator lock and said first arm to resiliently hold said first arm in said notch thereby forming a three part truss to rigidly position said sear actuator relative to said trigger.

8. The invention as defined in claim 7 whereby said operationally disposed means between said counter and said trigger includes a shoulder on said counter disposed for actuation against said actuator lock when the last round in the burst is fired to rotate said actuator lock for displacement of said first arm from said notch to break the rigid relationship of said sear actuator with said trigger and thereby permit release of said sear to the release position.

11. The invention as defined in claim 10 wherein said firing pin structure is of stepped configuration, a lip formed by said stepped configuration, and a tang extending rearwardly from said lip, said lip being engageable by said sear when in the engaging position for releasably retaining said firing pin in the cocked position, and said operator comprises a front arm having engagement with said lip during displacement of said firing pin from the recoil to the cocked position to thereby actuate said operator against the bias of said cooperating spring, and said front arm having contact with said tang in response to the subsequent displacement of said firing pin between the cocked and striking positions to retain said operator against rotation, and said front arm having registry with said recess during travel of said firing pin from the cocked to the recoil position to release said operator by said spring.

12. The invention as defined in claim 11 and including a plurality of notches formed around the circumference of said counter, a holding pawl rotatingly engageable with said notches to prevent counter rotation of said counter after being rotated by said actuating pawl, and including an arm having contact with said sear actuator to effect rotation of said holding pawl out of engagement with said notches when said trigger is released to the normal position thereof at the end of a burst.

13. The invention as defined in claim 12 wherein said inertia means comprises an inertia wheel, a lobe comprising a radial surface extending from the circumference of said inertia wheel, a lug extending from one side thereof, a circumferential cam riser and a spring biasing said inertia wheel for rotation in one direction, said radial surface being contactable by said front arm of said operator for transferring rotation thereof when energized by said firing pin to said inertial wheel for rotation thereof until the energy transferred thereto is absorbed by said spring, and wherein said sear is provided with a sear cam pivotally mounted thereon in the path of said cam riser during rotation of said inertia wheel, said sear cam being pivotally disposed to permit passage of said cam riser thereby during rotation of said inertia wheel under the influence of said spring thereby transferring the rotation of said inertia wheel to said sear for displacement thereof to the disengaged position.