Burst Fire Mechanism For Auto-loading Firearm

Abstract

An auto-loading firearm that may be fired semi-automatically and fully automatically is provided with a firing mechanism that permits bursts of, say, three rounds to be fired each time the trigger is pulled. The mechanism comprises a secondary sear disengager and interrupter support member pivotally mounted on the frame of the firearm so that upward movement of the forward end of the support member will cause the upper end of the secondary sear to move rearwardly out of engagement with the secondary sear notch of the hammer. An automatic fire activator link is pivotally mounted on an activator link positioner which, in turn, is pivotally mounted on the frame. The activator link positioner and the activator link are longitudinally movable to a rearwardmost, to an intermediate and to a forwardmost position, and the activator link is vertically movable to a lowermost and to an uppermost position. An indexing and interrupter assembly is rotatably mounted on the forward end of the support member, said assembly comprising an indexing ratchet having a predetermined number of ratchet teeth and an interrupter disc having at least one disengager arm contact surface and at least one disengager arm receiving notch. An indexing pawl is pivotally mounted on the hammer, the pawl engaging the teeth of the indexing ratchet and rotating said indexing and interrupter assembly one tooth at a time each time a cartridge is fired. When the activator link is at its rearwardmost position, it is out of engagement with the forward end of the support member, thereby permitting the secondary sear to remain in engagement with the secondary sear notch of the hammer after each round is fired. When the activator link is at its intermediate position, the activator link engages the rearward end of a rocker arm and is also moved into position to contact the interrupter disc. When the bolt of the firearm is closed the rearward end of the rocker arm is at its upper position and the activator link is brought into contact with the interrupter disc. When the bolt is moved rearwardly to its open position, the rearward end of the rocker arm moves downwardly and the activator link is moved out of contact with the interrupter disc. When the upwardly moving activator link contacts an arm contact surface of the interrupter disc, the secondary sear is moved out of engagement with the secondary sear notch and the firearm fires automatically. When the activator link enters an arm receiving notch of the interrupter disc, the secondary sear remains in engagement with the secondary sear notch and automatic firing is interrupted. When the activator link is at its forwardmost position, it contacts the interrupter disc and moves the support arm upwardly each time a round is fired, thereby firing the firearm automatically as long as the trigger is pulled.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to autoloading firearms, and in particular to a firing mechanism for such firearms capable of firing a burst comprising a predetermined number of rounds.

2. Prior Art

Auto-loading firearms, for example, automatic rifles, are well known in the art. Many such firearms, and in particular military arms, are designed to be fired both semi-automatically in which mode one round is fired each time the trigger is pulled and fully automatically in which mode the firearm fires continuously as long as the trigger is pulled. When the firearm is in its fully automatic mode of operation, it is frequently desirable to fire relatively short bursts of, say, three or four rounds per burst to conserve ammunition and to improve accuracy. Burst fire mechanisms for automatic firearms have heretofore been proposed. However, these prior burst fire mechanisms are generally overly complicated and unreliable, and in any case these mechanisms are generally unadaptable for use with the type of automatic firearm with which the present invention is concerned.

After an intensive investigation of the problems inherent in the design and functioning of burst fire mechanisms for auto-loading firearms, we have now devised an improved firing mechanism for such firearms which is versatile, reliable, and uncomplicated.

SUMMARY OF THE INVENTION

The burst fire mechanism of the invention is applicable to the general type of auto-loading firearms having a frame, a barrel secured to the frame, a bolt mounted for longitudinal travel in the frame behind the barrel, and an auto-loading mechanism for moving the bolt from its forward closed position to its rearward open position and return when the firearm is fired. The auto-loading mechanism may be of the gas operated, recoil operated, or blow-back type, provided rearward and forward movement of the bolt results directly or indirectly with a rocking movement of a rocker arm pivotally mounted on the frame. The pivotally mounted hammer is formed with a primary sear notch and with a secondary sear notch, and the pivotally mounted trigger is provided with a primary sear for engaging the primary sear notch of the hammer. A secondary sear is pivotally mounted on the frame for engaging the secondary sear notch of the hammer. The aforementioned rocker arm is pivotally mounted on the frame, the rearward end of rocker arm being moved upwardly when the bolt is at its forward closed position and being moved downwardly when the bolt is moved to its rearward open position. The upward and downward movement of the rocker arm alternately causes the secondary sear to be disengaged from and permitting the secondary sear to engage the secondary sear notch of the hammer.

The improved firing mechanism of the invention is capable of firing semi-automatically, fully automatically, and in bursts of predetermined duration. The firing mechanism comprises a secondary sear disengager and interrupter support member pivotally mounted on the frame. Upward movement of the forward end of the pivoted support member causes the upper end of the secondary sear to move rearwardly out of engagement with the secondary sear notch of the hammer. An indexing and interrupter assembly is rotatably mounted on the forward end of the support member, said assembly comprising an indexing ratchet having a predetermined number of ratchet teeth and an interrupter disc having at least one disengager arm contact surface and at least one disengager arm receiving notch. An indexing pawl is pivotally mounted on the hammer, said pawl engaging the teeth of said indexing ratchet and causing said indexing and interrupter assembly to rotate one tooth at a time each time a cartridge is fired. An activator link positioner is pivotally mounted on the frame for longitudinal movement to a rearwardmost to an intermediate and to a forwardmost position. An automatic fire activator link is pivotally mounted on the activator link positioner, said activator link having rocker arm engaging means adapted to engage the rearward end of the rocker arm and a secondary sear disengager arm adapted to contact the interrupter disc of the indexing and interrupter assembly, said rocker arm engaging means and said secondary sear disengager arm being movable forwardly and rearwardly by corresponding movement of the activator link positioner and being movable upwardly and downwardly when in engagement therewith. The secondary sear disengager arm moves the forward end of the secondary sear and interrupter support member upwardly to disengage the secondary sear when the disengager arm is moved forwardly by the activator link positioner and is moved upwardly by the rocker arm into contact with an arm contacting surface of the interrupter disc.

When the activator link positioner is moved to its rearwardmost position, the activator link is placed at its semiautomatic fire position at which the rocker arm engaging stud is out of engagement with the rearward end of the rocker arm and the disengager arm is out of position to contact the interrupter disc of the indexing and interrupter assembly.

When the activator link positioner is moved to its intermediate position, the activator link is placed at its burst fire position at which the rocker arm engaging stud is in engagement with the rearward end of the rocker arm and the forward end of the disengager arm is in position to contact the arm contact surfaces and to enter the arm receiving notches of the interrupter disc when the disengager arm is caused to move upwardly by the rocker arm. When the activator link positioner is moved to its forwardmost position the activator link is placed at its fully automatic fire position at which the rocker arm engaging stud is in engagement with the rearward end of the rocker arm and the forward end of the disengager arm is in position to contact the arm contact surfaces of the interrupter disc and is forward of the position at which it can enter the arm receiving notches of the interrupter disc when the disengager arm is caused to move upwardly by the rocker arm.

In an advantageous embodiment of the invention a manually movable firing mode selector is pivotally mounted on the frame, the selector being connected to the activator link positioner and being adapted to move the activator link positioner to its rearwardmost, its intermediate and its forwardmost positions. Other advantageous features of the firing mechanism of the invention will be apparent from the following detailed description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The improved firing mechanism of the invention will be better understood from the following description thereof in conjunction with the accompanying drawings of which:

FIG. 1 is a fragmentary side elevation of an auto-loading rifle embodying the invention.

FIG. 2 is a sectional view along an irregular vertical plane extending longitudinally through the receiver portion and the adjacent stock and forearm portions of the rifle of FIG. 1.

FIG. 3 is a fragmentary perspective view of the receiver showing the fire control selector and the rocker arm pivotally mounted thereon.

FIG. 3a is an exploded view of the fire control selector assembly.

FIG. 4 is a perspective view of the trigger housing assembly.

FIG. 5 is a perspective view of the rearward end of the receiver showing where the selector assembly is pivotally mounted thereon.

FIG. 6 is an exploded view of the trigger housing assembly of FIG. 4.

FIG. 7 is a sectional view along line 7--7 of FIG. 8 showing the fire control selector assembly as it is mounted on the receiver.

FIG. 8 is a fragmentary view of the firing mechanism, with parts broken away for better visibility, showing the firing mechanism in its burst fire mode at the start of the burst firing cycle with the trigger at rest and the hammer cocked and ready for firing.

FIG. 9 is a fragmentary view similar to FIG. 8 showing the firing mechanism in its burst fire mode in the middle of the burst firing cycle with the trigger pulled, the bolt open, and the hammer held temporarily by the secondary sear.

FIG. 10 is a fragmentary sectional view through the trigger and secondary sear showing the indexing ratchet and pawl mechanism and the indexing detent arrangement.

FIG. 11 is a fragmentary view similar to the left hand portion of FIG. 9 showing the firing mechanism in its burst fire mode in the middle of the burst firing cycle with the trigger pulled, the bolt closed, and the secondary sear moved rearwardly out of engagement with the secondary sear notch thereby releasing the hammer.

FIG. 12 is a fragmentary view similar to FIG. 11 showing the firing mechanism in its burst fire mode at the end of the burst firing cycle with the trigger pulled, the bolt closed, the disengager arm received in the disengager arm receiving notch of the interrupter disc, and the hammer held in its rearward position by the secondary sear.

FIG. 13 is a perspective view of the secondary sear, the interrupter and indexing ratchet assembly and the indexing pawl showing the relative positions of these parts.

FIG. 14 is a fragmentary view of the firing mechanism, with parts broken away for better visibility, showing the firing mechanism in its fully automatic mode in the middle of the automatic firing cycle with the trigger pulled, the bolt open, and the hammer held temporarily by the secondary sear.

FIG. 15 is a fragmentary view similar to FIG. 14 showing the firing mechanism in its fully automatic mode with the trigger pulled, the bolt closed, and the secondary sear withdrawn from engagement with the secondary sear notch, thereby releasing the hammer.

FIG. 16 is a fragmentary view of a modification of the secondary sear and interrupter support arm arrangement with portions of the trigger in section.

FIG. 17 is a perspective view of the modified secondary sear and interrupter support arm arrangement shown in FIG. 16.

FIG. 18 is an exploded view of the trigger and the secondary sear and interrupter support arm assembly shown in FIG. 17.

DETAILED DESCRIPTION

As shown best in FIG. 1, the principal externally visible components of a typical gas-operated auto-loading rifle of the type to which the present invention relates include a barrel 10, a receiver 11 to which the barrel is secured, a longitudinally movable bolt 12 mounted in the receiver 11 behind the barrel 10, a longitudinally movable slide 13 having a slide cocking handle 14 that is connected to the bolt 12, a trigger 15 and trigger guard 16, a magazine 17 and magazine latch 18, a stock 19 having a stock forearm 20, a forearm upperhand guard 21, a gas block 22 having a block clamp portion 23, a rear sight 24, and a safety activating lever 25. As shown in FIG. 2, the stock 19 is formed with a vertical slot or cut-out portion 26 in which the magazine 17 and the firing mechanism associated with the trigger 15 are received, and the stock forearm 20 is formed with a channel-shaped recess 27 in which the forward end of the slide 13 and the parts associated therewith are received.

Referring again to FIG. 2, the barrel 10 is formed with a bore 28 having a cartridge chamber 29 at the rearward end thereof. The longitudinally movable bolt 12 is provided with a firing pin 30 in position to strike a cartridge received in the chamber 29, an extractor (not shown) and a spring loaded ejector 32. The trigger 15 is pivotally mounted on the trigger housing 34 by means of the trigger pivot pin 35 that extends through the pivot hole 36 (shown best in FIG. 6) formed in the trigger 15. The trigger 15 is provided with a positioner pivot receiving slot 37, with a sear arm and primary sear 38 and with a trigger spring 39. Secondary sear 40 is also mounted on the pivot pin 35, the secondary sear being provided with a secondary sear spring 41. A hammer 42 is pivotally mounted on the housing 34 by means of the hammer pivot pin 43 in position to strike the rearward end of the firing pin 30 when the bolt 12 is in its closed position. The hammer 40 is provided with a rearwardly extending sear notch arm having a primary sear notch 45 and a secondary sear notch 46. A hammer strut 47 and spring 48 presses the hammer 42 toward its firing position as shown in FIG. 2. The receiver 11 and the parts associated therewith is inserted into the slot 26 from above and the trigger housing 34 and the parts associated therewith is inserted into the slot 26 from below, the receiver 11 and the housing 34 being secured together to form an assembly referred to herein and in the claims as the frame.

The magazine 17 is adapted to contain a plurality of cartridges 50 and is located in the slot 26 of the stock 19 directly below the bolt 12 when the bolt is in its closed position. The magazine 17 advantageously comprises a box-like structure that is removable from the slot 25, the magazine being held in position in the slot by the front magazine latch 51 and the manually operated rear magazine latch 18. A magazine follower 52 is disposed within the magazine 17 below the cartridge 50, the magazine follower having a follower spring (not shown) that presses the magazine follower upwardly, thereby moving the cartridge 50 into position to be loaded into the chamber 29 by the bolt 12.

As noted, the auto-loading mechanism is preferably gas operated, although other types of mechanisms (for example recoil and blow-back mechanisms) are well known in the art, the action shown in the drawings being a modification of the bolt and auto-loading mechanism of the M-14 rifle. In this modification a slide block (not shown) is located within the channel-shaped recess 27 of the forearm 20, the slide block being connected to the slide 13 and being held in its forward position by the slide spring 54 that is mounted on the slide spring guide rod 55. When the rifle is fired, powder combustion gases drive the slide block rearwardly against the pressure of the slide spring 54 thereby causing the bolt 12 to move rearwardly to its open position, the slide spring 54 then moving the bolt 12 forwardly to its closed position in a manner well known in the art.

The rifle may be fired in any of three distinct modes of operation -- namely, a semi-automatic mode in which one round is fired each time the trigger is pulled; a burst fire mode in which a burst of, say, three rounds is fired each time the trigger is pulled; and a fully automatic mode in which the rifle fires continuously as long as the trigger is pulled. A fire control selector 57 is pivotally mounted on the side of the receiver 11. When the selector 57 is at the position "S" shown in FIGS. 1, 2 and 3 the firing mechanism is placed in its semi-automatic mode of operation, when the selector 57 is at the position "B" shown in FIGS. 8, 9 and 12 the firing mechanism is placed in its burst fire mode of operation, and when the selector 57 is at the position "A" shown in FIGS. 14 and 15 the firing mechanism is placed in its fully automatic mode of operation.

In all modes of operation the firing mechanism is in its cocked and ready-to-fire condition when the hammer 42 is rotated rearwardly against the pressure of the hammer strut 47 and spring 48 so that the primary sear notch 45 is engaged and held by the primary sear 38, when a live cartridge is in the chamber 29 and when the bolt 12 is in its closed and locked position. When the firing mechanism is in its semi-automatic mode of operation, the trigger 15 is pulled to disengage the primary sear 38 from the primary sear notch 45, thereby allowing the hammer 42 to spring forward against the rearward end of the firing pin 30 which, in turn, strikes and fires the cartridge in the chamber 29. Powder combustion gases force the slide 13 and the bolt 12 rearwardly against the pressure of the slide spring 54. Rearward movement of the bolt 12 rotates the hammer 42 rearwardly so that the secondary sear notch 46 of the hammer is engaged and held by the secondary sear 40. The pressure of the slide spring 54 then causes the slide 13 and the bolt 12 to move forwardly to their closed positions. When the trigger 15 is released and allowed to return to its usual position, the primary sear notch 45 is engaged and held by the primary sear 38 while, at the same time, the secondary sear notch 46 is released by the secondary sear 40. The rifle is now again in its cocked and ready-to-fire position. This sequence of operations may be repeated one shot at a time until the magazine 17 is empty.

When the firing mechanism is in its burst fire mode of operation and is in its ready-to-fire condition, pulling the trigger 15 disengages the primary sear 38 from the primary sear notch 45 thereby releasing the hammer 42 and firing the cartridge in the chamber 29. Powder combustion gases force the slide 13 and the bolt 12 rearwardly against the pressure of the slide spring 54, and rearward movement of the bolt 12 rotates the hammer 42 rearwardly so that the secondary sear notch 46 of the hammer is engaged and held temporarily by the secondary sear 40. The pressure of the slide spring 54 then causes the slide 13 and the bolt 12 to move forwardly to the bolt closed position. As soon as the bolt 12 is closed and locked the automatic fire mechanism causes the secondary sear 40 to be disengaged from the secondary sear notch 46 thereby allowing the hammer 42 to spring forwardly and fire the fresh cartridge in the chamber 29 as in fully automatic operation. This sequence of operations is repeated automatically until a predetermined number of rounds of ammunition (say, three rounds) have been fired. When the predetermined number of rounds have been fired an automatic fire interrupter mechanism causes the secondary sear 40 to remain in engagement with the secondary sear notch 46 and to hold the hammer 42 in its cocked position after the bolt 12 is closed and locked. When the trigger is released and allowed to return to it usual position, the primary sear notch 45 of the hammer is engaged and held by the primary sear 38 while, at the same time, the secondary sear notch 46 is released by the secondary sear 40. Once again the rifle is in its cocked and ready-to-fire condition.

When the firing mechanism is in its fully automatic mode of operation and is in its ready-to-fire condition, pulling the trigger 15 disengages the primary sear 38 from the primary sear notch 45 which allows the hammer 42 to spring forward and fire the cartridge in the chamber 29. Rearward travel of the slide 13 and the bolt 12 rotates the hammer 42 rearwardly so that the secondary sear notch 46 is engaged and held temporarily by the secondary sear 40. When the bolt 12 moves forwardly to its closed and locked position the automatic fire mechanism disengages the secondary sear 40 from the secondary sear notch 46 thereby allowing the hammer 42 to spring forwardly and fire the fresh cartridge in the chamber 29. This sequence of operations is repeated until the trigger 15 released and allowed to return to its usual position at which position the primary sear notch 45 of the hammer 42 is engaged and held by the primary sear 38 of the trigger. As before, the rifle is again in its cocked and ready-to-fire condition.

As shown best in FIGS. 3 and 3a, the fire control selector assembly 57 comprises a selector thumb piece 58, a selector arm 59, a retaining pin 60, and a retaining pin detent spring 61 and plunger 62. The selector thumb piece is formed with a selector shaft receiving hole 63, a retaining pin groove 64, and a detent spring and plunger receiving hole 65. The selector arm 59 is provided wiJh a selector shaft 66 and with a positioner engaging stud 67, the shaft 66 being formed with a retaining pin receiving hole 68. The fire control selector assembly is mounted on the receiver 11 by inserting the shaft 66 into the shaft pivot hole 70 formed in the receiver (FIG. 5). The thumb piece 58 is then mounted on the shaft and the retaining pin 60 is inserted in the groove 64 and through the hole 68, the retaining pin 60 being held in place by the detent spring 61 and plunger 62 which have previously been inserted in the hole 65. When mounted on the receiver as shown in FIG. 3 the selector assembly 59 can be rotated to any one of the three positions marked S, B, or A (shown best in FIG. 5 of the drawing), the selector being detained in the selected position by the detent lug 71 on the inward facing surface of the thumb piece 58 which is releasably received in one of the detent recesses 72 formed in the receiver 11, as shown best in FIG. 7.

As shown best in FIGS. 2, 4, 6, and 8, an activator link positioner 73 is pivotally mounted on the trigger housing 34 by means of the positioner pivot stud 74. The positioner pivot stud 74 extends through the positioner pivot receiving slot 37 formed in the trigger 15 and serves as the backstop for the trigger spring 39. The activator link positioner 73 is provided with an activator pivot stud 75 on which the automatic fire activator link 76 is pivotally mounted and with a positioner engaging stud receiving slot 77 in which the positioner engaging stud 67 of the fire control selector 57 is received. The automatic fire activator link 76 is provided with a pivot hole 78 in which the activator pivot stud 75 is received, a rocker arm engaging stud 79, a secondary sear disengager arm 80, and a trigger pivot pin receiving slot 81. The activator link is also formed with preventer lug engaging surfaces 82, 83 and 84 as hereinafter described. A retaining ring 85 retains the activator pivot stud 75 in the pivot hole 78.

As shown best in FIGS. 3, 8 and 9, a longitudinally extending rocker arm 87 is pivotally mounted on the member 88 that depends from the right hand side of the receiver 11. The forward end of the rocker arm 87 is provided with a slide contacting finger 89 that extends upwardly through an opening 90 formed in the receiver 11 beneath the slide handle 14 of the slide 13, and the rearward end of the rocker arm 87 is provided with a fork-like member that is formed with a stud receiving slot 92 that is adapted to receive the rocker arm engaging stud 79 of the automatic fire activator link 76. A rocker arm spring 93 urges the rearward end of the pivoted rocker arm 87 downwardly and the forward end upwardly. The slide handle 14 is provided with a rocker arm depressor lug 94 which contacts the slide contacting finger 89 of the rocker arm 87 when the slide handle 14 is at its forwardmost position, the depressor lug 94 forcing the forward end of the rocker arm downwardly and the rearward end upwardly against the pressure of the spring 93 as shown in FIG. 8. When the slide handle 14 is moved rearwardly the rocker arm depressor lug 94 is moved out of contact with the slide contacting finger 89 of the rocker arm 87 thereby allowing the forward end of the rocker arm to move upwardly and the rearward end of the rocker arm to move downwardly as shown in FIG. 9.

It will be understood that other types of rocker arm engaging means may be substituted for the rocker arm engaging stud 79 of the activator link 76 and the stud receiving slot 92 of the rocker arm 87. For example, the positions of the stud 79 and slot 92 may be exchanged, or an idler link arrangement may be employed. Other equivalent rocker arm engaging means will be apparent to those skilled in the art.

As shown best in FIG. 2, when the fire control selector 5 is at its semi-automatic fire position "S", the activator link positioner 73 is rotated about the pivot stud 74 to its rearwardmost position, and the automatic fire activator link 76 is moved to its rearwardmost position at which position the trigger pivot pin 35 is received in the pin receiving slot 81 of the activator link and the rocker arm engaging stud 79 is out of engagement with the stud receiving slot 92 of the rocker arm 87. As shown best in FIGS. 8 and 9, when the fire control selector 57 is at its burst fire position "B", the activator link positioner 73 is rotated about the pivot stud 74 to a position intermediate its rearwardmost (FIG. 2) and its forwardmost (FIG. 14) positions, and the automatic fire activator link 76 is moved to its intermediate position at which position the trigger pivot pin 35 is moved out of engagement with the pin receiving slot 81 and the rocker arm engaging stud 79 is moved into engagement with the stud receiving slot 92 of the rocker arm 87. As shown best in FIGS. 14 and 15, when the fire control selector 57 is at its fully automatic fire position "A" the activator link positioner 73 is rotated about the pivot stud 74 to its forwardmost position, and the automatic fire activator link 76 is moved to its forwardmost position at which position the rocker arm engaging stud 79 is received in the stud receiving slot 92 of the rocker arm 87.

As shown in FIGS. 8 and 9 and in FIGS. 14 and 15, when the rocker arm engaging stud 79 of the automatic activator link 76 is received in the stud receiving slot 92 of the rocker arm 87, the activator link 76 is caused to move upwardly and then downwardly about the pivot-stud 75 when the rearward end of the rocker arm 87 is moved upwardly by the rocker arm depressor lug 94 and then downwardly by the rocker arm spring 93, as hereinbefore described. Upward and downward movement of the automatic fire activator link 76 about the pivot stud 75 causes the secondary sear disengager arm 80 of the activator link 76 to move upwardly and downwardly as hereinafter described.

A sear disengager and interrupter support member 96 is pivotally mounted on the trigger pivot pin 35. In the embodiment shown in FIGS. 2, 6 and 8 through 15 of the drawings, the support member 96 is an integrally formed part of the secondary sear 40 which, of course, is pivotally mounted on the pivot pin 35. In this embodiment the secondary sear spring 41 urges the secondary sear 40 forwardly into engagement with the secondary sear notch 46 of the hammer 42 and also urges the forward end of the integral support member 96 downwardly about the pivot pin 35. In the embodiment shown in FIGS. 16, 17 and 18 of the drawings, the support member 96a and the secondary sear 40a are separate parts both of which are pivotally mounted on the pivot pin 35. In this embodiment the secondary sear spring 41a urges the secondary sear 40a forwardly into engagement with the secondary sear notch 46 of the hammer 42 and a separate support member spring 97 urges the forward end of the separate support member 96a downwardly about the pivot pin 35.

In both embodiments, upward movement of the support member 96 or 96a causes the secondary sear 40 or 40a to move rearwardly against the pressure of the secondary sear spring 41 or 41a, respectively, and out of engagement with the secondary sear notch 46 of the hammer 42. In the first embodiment, the support member 96 is an integrally formed part of the secondary sear 40. In the second embodiment, the support member 96a is provided with a secondary sear stop surface 98 that is contacted by the laterally extending stop engaging lug 99 of the secondary sear 40a so that, when the support member 96a is moved upwardly about the pivot pin 35, the secondary sear 40a is moved rearwardly about the pivot pin 35. Conversely, forward movement of the secondary sear 40 or 40a beyond a predetermined point is prevented by blocking downward movement of the integral support member 96 or the separate support member 96a by means of the support member lifting lug 100 of the trigger 15. The support members 96 and 96a are caused to move upwardly, and thereby to disengage the secondary sear 40 or 40a, by the support member lifting lug 100 of the trigger 15 or by the secondary sear disengager arm 80 of the activator link 76, as hereinafter described.

A burst fire indexing and interrupter assembly is rotatably mounted on the forward end of the interrupter support members 96 and 96a. As shown best in FIGS. 6, 10, 13 and 18, the indexing and interrupter assembly comprises an interrupter shaft 102 having an interrupter disc 103 secured to one end thereof and having an indexing ratchet 104 mounted on the ratchet stud 105 at the opposite end thereof and secured thereto by the ratchet pin 106. The interrupter shaft 102 is rotatably mounted in the shaft receiving hole 107 formed in the forward end of the support member 96 (and support member 96a). The indexing ratchet 104 is formed with a predetermined number (for example, six) of ratchet teeth 108, and the interrupter shaft 102 is formed with a corresponding number of interrupter detent recesses 109. A detent plunger 110 and spring 111 is received in the plunger receiving hole 112 formed in the support member 96, the spring pressed plunger 110 engaging one of the detent recesses 109 in the interrupter shaft 102 to releasably detain the indexing ratchet 104 and interrupter disc 103 at a given index position.

The outer periphery of the interrupter disc 103 is provided with secondary sear disengager arm contact surfaces 114 and with secondary sear disengager arm receiving notches 115. When the interrupter disc 103 is rotated to a position at which the disengager arm contact surface 114 is directly above the end of the disengager arm 80 as shown in FIGS. 9 and 11, and when the disengager arm 80 is moved upwardly by the action of the rocker arm 87 as shown in FIG. 11, the disengager arm 80 will contact the arm contact surface 114 and move the end of support member 96 upwardly about the pivot pin 35. As previously noted, when the secondary sear notch 46 is engaged by the secondary sear 40 (or 40a) upward movement of the support member 96 (and 96a) moves the secondary sear 40 (and 40a) rearwardly about the pivot pin 35 and out of engagement with the secondary sear notch 46 of the hammer 42. When the interrupter disc 103 is rotated to a position at which one of the arm receiving notches 115 is directly above the end of the disengager arm 80 as shown in FIG. 12, upward movement of the disengager arm 80 caused by the action of the rocker arm 87 will move the end of the disengager arm into the arm receiving notch 115 and thereby avoid upward movement of the forward end of the support member 96 with concomittant disengagement of the secondary sear 40.

An indexing pawl 117 having a ratchet engaging pawl tooth 118 is pivotally mounted on the hammer 42 by means of the pawl pivot pin 119 in position to engage the ratchet teeth 108 of the indexing ratchet 104. As shown best in FIGS. 6 and 10, a pawl support pin 120 on the inner surface of the safety 25 supports the pawl 117 and maintains the pawl tooth 118 in position to engage the ratchet teeth 108 of the indexing ratchet 104. In addition, a pawl spring 121 may be provided which urges the pawl 117 upwardly against the indexing ratchet 104 and thereby helps maintain the pawl tooth 118 in engagement with the ratchet teeth.

When the hammer 42 is in its forward position as shown in FIGS. 2 and 4 and in outline in FIG. 10, the pawl tooth 118 of the indexing pawl 117 is out of engagement with the ratchet teeth 108 of the indexing ratchet 104. As shown best in FIG. 10, when the rifle is fired (or manually cocked), the hammer 42 rotates rearwardly to its cocked position thereby causing the pawl tooth 118 to engage one of the teeth 108 of the indexing ratchet 104 and to rotate the indexing ratchet a predetermined fractional part of a complete revolution (in the present case, one-sixth of a complete revolution). The spring loaded detent plunger 110 engages the corresponding detent recess 109 to prevent further rotation of the indexing ratchet 104. Thus, it will be seen that each time the rifle is fired the indexing pivot 117 will cause the indexing ratchet 104 and the interrupter disc 103 to rotate an angular distance equivalent to the angular spacing of the ratchet teeth 108, one tooth at a time. That is to say, when the rifle is in its semi-automatic mode of operation the indexing ratchet 104 and the interrupter disc 103 will be rotated an angular distance equivalent to the angular distance between the teeth 108 of the ratchet 104 each time the trigger 15 is pulled. When the rifle is in its burst fire mode of operation the indexing ratchet 104 and interrupter disc 103 will be rotated on an angular distance corresponding to the number of rounds fired in each burst. When the rifle is in its fully automatic mode of operation, the rifle will fire continuously as long as the trigger 15 is pulled and the indexing ratchet 104 and interrupter disc 103 will be rotated an angular distance corresponding to the number of rounds that are fired.

When the rifle is in its burst fire mode of operation, the number of rounds fired in each burst (that is, each time the trigger is pulled) is determined by the number of ratchet teeth 108 on the indexing ratchet 104 and by the number of disengager arm receiving notches 115 formed in the interrupter disc 103. Automatic fire is interrupted when the interrupter disc 103 is rotated to the position at which the disengager arm 80 will enter an arm receiving notch 115 formed in the interrupter disc. In the embodiment shown in the drawings, the indexing ratchet 104 is formed with six ratchet teeth 108 and the interrupter disc 103 is formed with two disengager arm receiving notches 115. As a consequence, every time the rifle fires one round the indexing ratchet 104 and the interrupter disc 103 will be rotated one-sixth of a revolution, and after three rounds the interrupter disc will have been rotated one-half a revolution to bring one of the arm receiving notches 115 into position to receive the end of the disengaging arm 80 and thereby interrupt the automatic firing of the rifle. The system permits great versatility in the length of the burst fire sequence. For example, the combination of an indexing ratchet 104 having six ratchet teeth 108 with an interrupter disc 103 having three equally spaced arm receiving notchs 115 would provide a burst of two rounds each time the trigger is pulled; the combination of an indexing ratchet having eight ratchet teeth 108 with an interrupter disc having two arm receiving notches 115 would provide a burst of four rounds; the combination of an indexing ratchet having five ratchet teeth 108 with an interrupter disc having one arm receiving notch 115 would provide a burst of five rounds; and so on up to the limit imposed by the physical dimensions of the parts involved. Moreover, the burst fire mode of operation can be eliminated by providing an interrupter disc 103 having no arm receiving notches, and the fully automatic mode of operation can be eliminated by blocking movement of the fire control selector 57 or the activator link positioner 73 or the automatic fire activator link 76 into their respective automatic fire positions.

As previously noted, the firing mechanism is in its cocked and ready-to-fire condition when the hammer is rotated rearwardly against the pressure of the spring loaded hammer strut 47 so that the primary sear notch 45 is engaged and held by the primary sear 38, when a live cartridge is in the chamber 29, and when the bolt 12 is in its closed and locked position. This ready-to-fire condition of the rifle is shown best in FIG. 8 in connection with the burst fire mode of operation.

When the fire control selector knob 57 is rotated to the position "S" as shown in FIGS. 1, 2 and 3, the firing mechanism is placed in its semi-automatic mode of operation. In its semi-automatic mode, the activator link positioner 73 is at its rearwardmost position, and the automatic fire activator link 76 is also at its rearwardmost position at which position the trigger pivot pin 35 is received in the pin receiving slot 81 of the activator link and the rocker arm engaging stud 79 is out of engagement with the stud receiving slot 92 of the rocker arm 87. When the firing mechanism is in its ready-to-fire condition, the trigger 15 is pulled to disengage the primary sear 38 from the primary sear notch 45 thereby allowing the hammer 42 to spring forward against the rearward end of the firing pin 30 which, in turn, strikes and fires the cartridge in the chamber 29. Pulling the trigger 15 rearwardly about the pivot pin 35 moves the support member lifting lug 100 downwardly a corresponding distance, thereby allowing the support member 96 (or 96a) to move downwardly and the secondary sear 40 (or 40a) to move forwardly into position to engage the secondary sear notch 46 of the hammer 42. In addition, rearward movement of the trigger 15 moves the activator movement preventer lug 123 into engagement with the preventer receiving surface 82 thereby preventing movement of the activator link positioner 73 when the rifle is fired.

When the cartridge is fired, powder combustion gases force the slide 13, the slide handle 14 and the bolt 12 from their forward closed positions to their rearward positions. Rearward movement of the slide handle 14 allows the forward end of the rocker arm 87 to move upwardly which causes the rearward end of the rocker arm to move downwardly from its upper position to its lower position as previously described. However, as the rocker arm engaging stud 79 of the activator link 76 is out of engagement with the stud receiving slot 92 of the rocker arm 87, the downward movement of the rearward end of the rocker arm has no effect on the firing sequence. Rearward movement of the bolt 12 extracts and ejects the spent cartridge case and also rotates the hammer 42 rearwardly so that the secondary sear notch 46 of the hammer is engaged and held by the secondary sear 40 (or 40a).

The pressure of the slide spring 54 then causes the slide 13 to move forwardly carrying with it the slide handle 14 and the bolt 12. As the bolt 12 moves from its open position to its closed position, it picks up a fresh cartridge 50 from the magazine 17 and inserts the cartridge in the chamber 29 in the manner known in the art. When the slide handle 14 reaches its forward closed position, the depressor lug 94 forces the forward end of the rocker arm 87 downwardly which moves the rearward end of the rocker arm upwardly as previously described. However, as the rocker arm engaging stud 79 is out of engagement with the stud receiving slot 92, upward movement of the rearward end of the rocker arm 87 has no effect on the firing sequence. When the trigger 15 is released and allowed to return to its usual position, the primary sear notch 45 of the hammer is engaged and held by the primary sear 38 of the trigger while, at the same time, the secondary sear notch 46 is released by the secondary sear 40 (or 40a). That is to say, forward movement of the trigger 15 to its usual position causes the support member lifting lug 100 to move upwardly a corresponding distance thereby moving the support member 96 (or 96a) upwardly and the secondary sear 40 (or 40a ) rearwardly out of engagement with the secondary sear notch 46. The rifle is now once again in its cocked and ready-to-fire position. This sequence of operations may be repeated one shot at a time until the magazine 17 is empty.

When the fire control selector knob 57 is rotated to the position "B" as shown in FIGS. 8, 9, 11 and 12, the firing mechanism is placed in its burst fire mode of operation. In its burst fire mode, the activator link positioner 73 and the automatic fire activator link 76 are at their intermediate position at which position the trigger pivot pin 35 is moved out of engagement with the pin receiving slot 81 of the activator link and the rocker arm engaging stud 79 is moved into engagement with the stud receiving slot 92 of the rocker arm 87, as shown best in FIG. 8. In addition, the secondary sear disengager arm 80 is moved forwardly into position to be received in the arm receiving notch 115 of the interrupter disc 103 as shown in FIGS. 8 and 12 and to contact the arm contact surface 114 of the interrupter disc 103 as shown in FIGS. 9 and 11.

When the firing mechanism is in its ready-to-fire condition as shown in FIG. 8, the trigger 15 is pulled to disengage the primary sear notch 45 thereby allowing the hammer 42 to spring forward against the rearward end of the firing pin 30 which, in turn, strikes and fires the cartridge in the chamber 29. Pulling the trigger 15 rearwardly about the pivot pin 35 moves the support member lifting lug 100 downwardly a corresponding distance, thereby allowing the support member 96 to move downwardly and the secondary sear 40 to move forwardly into position to engage the secondary sear notch 46 of the hammer 42. In addition, rearward movement of the trigger 15 moves the activator movement preventer lug 123 into engagement with the preventer receiving surface 83 as shown in FIG. 9.

Powder combustion gases force the slide 13, the slide handle 14 and the bolt 12 rearwardly against the pressure of the slide spring 54. As shown in FIG. 9, rearward movement of the slide handle 14 allows the forward end of the rocker arm 87 to move upwardly which causes the rearward end of the rocker arm to move downwardly to its lower position. Because the rocker arm engaging stud 79 of the activator link 76 is in engagement with the stud receiving slot 92 of the rocker arm 87, the downward movement of the rearward end of the rocker arm causes the activator link 76 to be rotated downwardly about the pivot stud 75 which, in turn, moves the secondary sear disengager arm 80 downwardly out of contact with the interrupter disc 103. Rearward movement of the bolt 12 rotates the hammer 42 rearwardly about the pivot pin 43 so that the secondary sear notch 46 of the hammer is engaged and temporarily held by the secondary sear 40, as shown in FIG. 9. At the same time, as shown best in FIG. 10, the tooth 118 of the indexing pawl 117 engages one of the ratchet teeth 108 of the indexing ratchet 104 thereby causing the indexing ratchet 104 and the interrupter disc 103 to rotate an angular distance equivalent to the spacing of the ratchet teeth 108. This rotation moves the interrupter disc 103 from the position shown in FIG. 8 to the position shown in FIG. 9 at which the arm contact surface 114 of the interrupter disc is in position to be contacted by the disengager arm 80 of the activator link 76.

The pressure of the slide spring 54 causes the slide 13 to move forwardly carrying with it the slide handle 14 and the bolt 12. When the slide handle 14 reaches its forward closed position, the depressor lug 94 forces the forward end of the rocker arm 87 downwardly which moves the rearward end of the rocker arm upwardly, as previously described. As shown best in FIG. 11, upward movement of the rearward end of the rocker arm 87 moves the activator link 76 upwardly about the pivot stud 75 which, in turn, causes the secondary sear disengager arm 80 to contact the arm contact surface 114 of the interrupter disc 103 and to move the forward end of the interrupter support member 96 upwardly about the trigger pin 35. In the embodiment shown in FIGS. 8 to 13, the support member 96 is an integral part of the secondary sear 40 so that upward movement of the support member 96 causes the secondary sear 40 to move rearwardly out of engagement with the secondary sear notch 46 of the hammer 42. In the embodiment shown in FIGS. 16 to 18, the support member 96a and the secondary sear 40a are separate parts both pivoted on the pivot pin 35. Upward movement of the support member 96a moves the secondary sear 40a rearwardly out of engagement with the secondary sear notch 46 as previously described. When the secondary sear notch 46 is disengaged as shown in FIG. 11, the hammer 42 is released and strikes the firing pin 30 which, in turn, strikes and fires the cartridge in the chamber 29.

When the cartridge is fired, the slide 13, slide handle 14 and bolt 12 move rearwardly and then forwardly to repeat the sequence of operations described in the preceding two paragraphs. The rifle is now firing automatically. After three rounds are fired, the interrupter disc 103 is rotated to the position shown in FIG. 12 at which position the disengager arm 80 is received in the arm receiving notch 115 of the interrupter disc. As a result, upward movement of the rearward end of the rocker arm 87 with concomitant upward movement of the disengager arm 80 does not move the forward end of the support member 96 (or 96a) upwardly and does not disengage the secondary sear 40 (or 40a) and the secondary sear notch 46. Automatic firing of the rifle thereupon is interrupted or stopped. When the trigger 15 is released and allowed to return to its usual position, the primary sear notch 45 of the hammer is engaged and held by the primary sear 28 of the trigger while, at the same time, the secondary sear notch 46 is released by the secondary sear 40 (or 40a) in the manner previously described. The rifle is once again in its cocked and ready to fire condition as shown in FIG. 8.

When the fire control selector knob 57 is rotated to the position "A" as shown in FIGS. 14 and 15, the firing mechanism is placed in its automatic mode of operation. In its automatic mode, the activator link positioner 73 and the automatic fire activator link 76 are at their forwardmost position at which position the trigger pivot pin 35 is out of engagement with the pin receiving slot 81 of the activator link and the rocker arm engaging stud 79 is in engagement with the stud receiving slot 92 of the rocker arm 87. In addition, as shown in FIGS. 14 and 15, the secondary sear disengager arm 80 is moved forwardly beyond the point at which it can be received in the arm receiving notch 115 of the interrupter disc 103, the disengager arm 80 being in position to contact the arm contact surface 114 of the interrupter disc 103 as also shown in FIGS. 14 and 15.

When the firing mechanism is in its ready-to-fire condition (corresponding to the condition shown in FIG. 8), the trigger 15 is pulled to disengage the primary sear 38 from the primary sear notch 45 thereby allowing the hammer 42 to spring forward against the rearward end of the firing pin 30 which, in turn, strikes and fires the cartridge in the chamber 29. Pulling the trigger 15 rearwardly about the pivot pin 35 moves the support member lifting lug 100 downwardly a corresponding distance, thereby allowing the support member 96 to move downwardly and the secondary sear 40 to move forwardly into position to engage the secondary sear notch 46 of the hammer 42. In addition, rearward movement of the trigger 15 moves the activator movement preventer lug 123 into engagement with the preventer receiving surface 84 as shown in FIG. 14.

Powder combustion gases force the slide 13, the slide handle 14 and the bolt 12 rearwardly against the pressure of the slide spring 54. As shown in FIG. 14, rearward movement of the slide handle 14 allows the forward end of the rocker arm 87 to move upwardly which causes the rearward end of the rocker arm to move downwardly to the lower position. Because the rocker arm engaging stud 79 of the activator link 76 is in engagement with the stud receiving slot 92 of the rocker arm 87, the downward movement of the rearward end of the rocker arm causes the activator link 76 to be rotated downwardly about the pivot stud 75 which, in turn, moves the secondary sear disengager arm 80 downwardly out of contact with the interrupter disc 103 as shown in FIG. 14. Rearward movement of the bolt 12 rotates the hammer 42 rearwardly about the pivot pin 43 so that the secondary sear notch 46 of the hammer is engaged and temporarily held by the secondary sear 40, as shown in FIG. 14. At the same time, the tooth 118 of the indexing pawl 117 engages one of the ratchet teeth 108 of the indexing ratchet 104 thereby causing the indexing ratchet 104 and the interrupter disc 103 to rotate an angular distance equivalent to the spacing of the ratchet teeth 108. However, this rotation of the interrupter disc 103 has no effect on the firing sequence as the secondary sear disengager arm 80 has been moved forwardly beyond the point at which it can enter the arm receiving notches 115 formed in the interrupter disc 103.

The pressure of the slide spring 54 causes the slide 13 to move forwardly carrying with it the slide handle 14 and the bolt 12. When the slide handle 14 reaches its forward closed position, the depressor lug 94 forces the forward end of the rocker arm 87 downwardly which moves the rearward end of the rocker arm upwardly, as previously described. As shown best in FIG. 15, upward movement of the rearward end of the rocker arm 87 moves the activator link 76 upwardly about the pivot stud 75 which, in turn, causes the secondary sear disengager arm 80 to contact the arm contact surface 114 of the interrupter disc 103 and to move the forward end of the interrupter support member 96 upwardly about the trigger pin 35. In the embodiment shown in FIGS. 14 and 15, the support member 96 is an integral part of the secondary sear 40 so that upward movement of the support member 96 causes the secondary sear 40 to move rearwardly out of engagement with the secondary sear notch 46 of the hammer 42. In the embodiment shown in FIGS. 16 to 18, support member 96a and the secondary sear 40a are separate parts both pivoted on the pivot pin 35. Upward movement of the support member 96a causes the secondary sear stop surface 98 to contact the stop engaging lug 99 of the secondary sear 40a and to move the secondary sear rearwardly out of engagement with the secondary sear notch of the hammer 42. When the secondary sear notch 46 is disengaged as shown in FIG. 15, the hammer 42 is released and strikes the firing pin 30 which, in turn, strikes and fires the cartridge in the chamber 29.

When the cartridge is fired, the slide 13, slide handle 14 and bolt 12 move rearwardly and then forwardly to repeat the sequence of operations described in the preceding two paragraphs. The rifle will continue to fire automatically in the manner described as long as the trigger remains pulled and the ammunition holds out. When the trigger 15 is released and allowed to return to its usual position, the primary sear notch 45 of the hammer is engaged and held by the primary sear 38 of the trigger while, at the same time, the secondary sear notch 46 is released by the secondary sear 40 in the manner previously described. The rifle is once again in its cocked and ready-to-fire condition.

The automatic rifle shown in the drawings is designed to be readily assembled and disassembled, either in the shop or in the field. All parts of the firing mechanism are securely mounted either on the receiver 11 or on the trigger housing 34 as shown in FIGS. 3 and 4 of the drawings. As previously noted, the receiver 11 and the parts associated therewith are inserted into the slot 26 of the stock 19 from above and the trigger housing 34 and the parts associated therewith are inserted into the slot 26 from below, the receiver and trigger housing being secured together by the hook-like elements 125 of the trigger guard 16 in the manner known in the art. The parts mounted on the receiver 11 that are intended to cooperate with other parts mounted on the trigger housing 34 are designed to mesh or mate together automatically, as exemplified by the automatic engagement of the positioner engaging stud 67 by the stud receiving slot 77 when the receiver 11 and the trigger housing 34 are secured together. When thus secured together the receiver 11 and the trigger housing 34 comprise a structure referred to herein and in the claims as the frame of the firearm.

The various parts of the firing mechanism are advantageously organized into sub-assemblies which are mounted either on the trigger housing 34 or on the receiver 11. For example, the activator link positioner 73 and the automatic fire activator link 76 comprise one such sub-assembly, and the interrupter member 96 and the indexing and interrupter assembly 102-110 comprise another such sub-assembly, both mounted on the trigger housing 34. The sub-assembly concept is particularly well exemplified by the trigger, secondary sear and interrupter support member sub-assembly shown in FIGS. 16, 17, and 18 in which the various parts are first pivotally assembled on the assembly bushing 127 as shown best in FIG. 17 before being pivotally mounted on the trigger housing 34 by means of the trigger pivot 35 as shown in FIG. 16. In this embodiment, the pivot hole portion 128 of the trigger 15 is adapted to be received between the pair of downwardly extending pivot hole portions 129 of the support member 96a, and the pivot hole portion 130 of the secondary sear 40a is adapted to be received in the upper secondary sear receiving slot 131 formed in the support member 96a and in the lower secondary sear receiving slot 132 formed in the trigger 15. To assemble the parts the support member spring 97 is placed in the spring receiving holes 133 and 134 formed in the trigger 15 and in the support member 96a, respectively, and the assembly bushing 127 is inserted through the pivot hole 136 formed in one of the dependant pivot portions 129 of the support member 96a and through the adjacent trigger pivot hole 36 of the trigger 15. The secondary sear spring 41a is then inserted in the spring receiving hole 138 formed in the trigger 15 and the pivot hole portion 130 of the secondary sear 40a is inserted into the upper and lower secondary sear receiving slots 131 and 132. The assembly bushing 127 is then completely inserted through the pivot hole 140 of the secondary sear and the pivot holes 36 and 136 of the trigger 15 and support member 96a as shown in FIG. 17. The resulting assembly is then mounted on the trigger housing as shown in FIG. 16.

Claims

We claim:

1. In an auto-loading firearm having a frame, a barrel secured to the frame, a bolt mounted for longitudinal travel in the frame behind the barrel, an auto-loading mechanism connected to the bolt for moving the bolt from its forward closed position to its rearward open position and return when the firearm is fired, a hammer pivotally mounted on the frame, said hammer being formed with a primary sear notch and with a secondary sear notch, a trigger pivotally mounted on the frame, said trigger having a primary sear for engaging the primary sear notch of the hammer, a secondary sear pivotally mounted on the frame for engaging the secondary sear notch of the hammer, a rocker arm pivotally mounted on the frame, the rearward end of the pivoted rocker arm being moved upwardly when the bolt is at its forward closed position and being moved downwardly when the bolt is moved to its rearward open position, said upward and downward movement of the rocker arm alternately causing the secondary sear to be disengaged from and permitting the secondary sear to engage the secondary sear notch of the hammer, the improvement which comprises a firing mechanism capable of firing semi-automatically, fully automatically and in bursts of predetermined duration, said mechanism comprising:

a secondary sear disengager and interrupter support member pivotally mounted on the frame, upward movement of the forward end of said pivoted support member causing the upper end of the secondary sear to move rearwardly out of engagement with the secondary sear notch of the hammer,

an indexing and interrupter assembly rotatably mounted on the forward end of said support member, said assembly comprising an indexing ratchet having a predetermined number of ratchet teeth and an interrupter disc having at least one disengager arm contact surface and at least one disengager arm receiving notch,

an indexing pawl pivotally mounted on the hammer, said pawl engaging the teeth of said indexing ratchet and causing said indexing and interrupter assembly to rotate one tooth at a time each time a cartridge is fired,

an activator link positioner pivotally mounted on the frame for longitudinal movement to a rearwardmost, to an intermediate and to a forwardmost position,

an automatic fire activator link pivotally mounted on said activator link positioner, said activator link having a rocker arm engaging means adapted to engage the rearward end of said rocker arm and a secondary sear disengager arm adapted to contact the interrupter disc of the indexing and interrupter assembly, said rocker arm engaging means and said secondary sear disengager arm being movable forwardly and rearwardly by corresponding movement of the activator link positioner and being movable upwardly and downwardly by corresponding movement of said rocker arm when in engagement therewith, said secondary sear disengager arm moving the foreward end of said support member upwardly to disengage said secondary sear when said disengager arm is moved forwardly and upwardly into contact with an arm contact surface of said interrupter disc,

said activator link positioner being moved to its rearwardmost position to place the activator link at its semi-automatic fire position at which the rocker arm engaging means is out of engagement with the rearward end of the rocker arm and the disengager arm is out of position to contact the interrupter disc of the indexing and interrupter assembly,

said activator link positioner being moved to its intermediate position to place the activator link at its burst fire position at which the rocker arm engaging means is in engagement with the rearward end of the rocker arm and the forward end of the disengager arm is in position to contact the arm contact surfaces and to enter the arm receiving notches of the interrupter disc when the disengager arm is caused to move upwardly by the rocker arm, and

said activator link positioner being moved to its forwardmost position to place the activator link at its fully automatic fire position at which the rocker arm engaging means is in engagement with the rearward end of the rocker arm and the forward end of the disengager arm is in position to contact the arm contact surfaces of the interrupter disc and is forward of the position at which it can enter the arm receiving notches of the interrupter disc when the disengager arm is caused to move upwardly by the rocker arm.

2. The firearm according to claim 1 in which a manual movable firing mode selector is pivotally mounted on the frame, said selector being connected to the activator link positioner and being movable about its pivotal mounting to move said activator link positioner to its rearwardmost, its intermediate and its forwardmost positions.

3. The firearm according to claim 1 in which the secondary sear disengager and interrupter support member is secured to the secondary sear, whereby upward movement of the forward end of said support member moves the upper end of the secondary sear rearwardly out of engagement with the secondary sear notch of the hammer.

4. The firearm according to claim 1 in which the secondary sear and the secondary sear disengager and interrupter support member are independently pivotally mounted on the frame, in which said support member is formed with a secondary sear stop surface and in which said secondary sear is formed with a stop engaging lug, said stop engaging lug normally contacting said secondary sear stop surface, whereby upward movement of the forward end of said support member causes the upper end of the secondary sear to move rearwardly.

5. The firearm according to claim 1 in which the trigger is provided with a support member lifting lug that normally is in contact with the secondary sear disengager and interrupter support member, forward movement of the trigger causing the support member lifting lug to move the forward end of said support member upwardly and thereby move the upper end of the secondary sear rearwardly out of engagement with the secondary sear notch of the hammer.

6. The firearm according to claim 1 in which the trigger is provided with an activator movement preventer lug that is adapted to move into engagement with a first preventer receiving surface formed in the activator link when the activator link is at its rearwardmost position, into engagement with a second preventer receiving surface formed in said activator link when said activator link is at its intermediate position, and into engagement with a third preventer receiving surface formed in the activator link when said activator link is at its forwardmost position.

7. The firearm according to claim 1 in which the interrupter disk is formed with at least one disengager arm receiving notch, and in which the indexing ratchet is formed with at least two ratchet teeth.

8. The firearm according to claim 1 in which the interrupter disk is formed with at least two disengager receiving notches and in which the indexing ratchet is formed with a number of ratchet teeth that is a multiple of the number of said disengager arm receiving notches.

9. The firearm according to claim 1 in which the indexing and interrupter assembly is provided with a detent that releasably detains said assembly from further rotation after said assembly has been rotated an angular distance equivalent to one ratchet tooth by the indexing pawl.

10. The firearm according to claim 1 in which the automatic fire activator link is formed with a trigger pivot pin receiving slot that is adapted to engage the pivot pin on which the trigger is pivotally mounted when said activator link is at its rearwardmost position, said pivot pin receiving slot being moved out of engagement with the said pivot pin when the activator link is moved forwardly to its intermediate position.