Nov. 9, 1971 R. D. PLUMER ET All- 3,618,455 MANUAL OF EN AND CLOSED WEAPON FIRE CONCROL WITH AUTOMATIC HEAT RESPONSIVE OWERRIDE Filed July 25, 1969

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foy (2/imer,INVIENIORS. & BY throa Shroud 6.42724.4 ATTORNEY 3,618,455 United States Patent Office Patented Nov. 9, 1971 2 a position to provide automatic closed-bolt operation of 3,618,455 MANUAL OPEN AND CLOSED-BOLT WEAPON the ; FIRE CONTROL WITH AUTOMATIC HEAT FIG. 3 is a view like FIG. 2 but illustrating the fire con RESPONSEVE OVERRIDE trol cam in a position to provide an automatic open-bolt Roy D. Plumer, Santa Barbara, and Harold Shrout, mode of operation for the firearm; and Goleta, Calif., assignors to General Motors Corp0 FIG. 4 is a view like FIGS. 2 and 3 but illustrating the ration, Detroit, Mich. fire control cam in a position to provide a semiautomatic Filed July 25, 1969, Ser. No. 844,926 closed-bolt mode of operation for the firearm. Int, C. F41d 11/02, 1 1/20 Referring now to the drawings and more particularly U.S. C. 89-132 3 Claims 10 to FIG. 1 a firearm which takes the form of a is illus trated and is generally designated by reference numeral 10. This firearm includes a receiver 12 and a barrel 4 ABSTRACT OF THE DISCLOSURE Suitably connected to the receiver. The firearm has a stock A fire control system for an capable which is not illustrated and has a housing 16 which sup of being manually set to selectively provide automatic 5 ports the trigger 18 and a plurality of sear parts forming closed-bolt operation, automatic open-bolt operation and a fire control mechanism which is to be described. The semiautomatic closed-bolt operation. The firearm can be housing 6 can be a separate assembly or can be a part set to these modes of operation by moving a mode-Selector of the receiver body 12 insofar as the fire control aspects knob located on the exterior of the firearm. The knob of this invention are concerned. moves a cam which cooperates with sear parts to set the 20 The barrel 4 has a bore 14A provided with suitable mode of operation. A heat sensing device is positioned in rifling, not illustrated, and this bore 14A communicates the barrel of the firearm near the firing to sense with a firing chamber 14B. The firing chamber 14B con the temperature of the barrel and when this temperature tains an obturator, which is not illustrated, that engages reaches a point at which cook-off of a is incipient an end wall 20B of a reciprocable bolt designated by a mechanism is actuated to automatically switch the fire 25 reference numeral 20. The obturator can take the form of arm to its automatic open-bolt mode of operation. The a hollow cylindrical member having a section engaging firearm is capable of firing caseless ammunition. the inner wall of chamber 14B and having an end section tightly engaging the Wall 20B of the bolt when the bolt is closed. This arrangement is provided so that the firearm The invention herein described was made in the course 30 will be capable of firing so-called caseless ammunition of work under a contract or subcontract thereunder with which has no metallic case. The method of obturation the Department of the Army. forms no part of the present invention however and the This invention relates to fire control systems for fire fire control mechanism of this invention could be used arms and more particularly to a fire control system which with firearms using a case type of ammunition. can be selectively set to provide a plurality of modes of 35 The bolt 20 carries a firing pin 22 which passes through operation and wherein the firearm is switched to an auto the bolt 20 and a bolt carrier 24. The firing pin is moved matic open-bolt mode whenever the temperature of the forward to strike the primer of a cartridge when the end firearm reaches a condition wherein cook-off of a cartridge 22A of the firing pin is struck by a hammer, to be de is incipient. scribed. The bolt 20 and the bolt carrier 24 are so con It is known in the art of firearms that after repeated 40 nected that the bolt can be rotated as the parts are re and continuous firing of the weapon the temperature of ciprocated by a suitable cam slot and follower arrange the weapon may rise to a point where a cartridge is fired ment which is not illustrated to permit locking lugs 20A due to high temperature and without being struck by the on the bolt to pass through slots 14C formed in the barrel. firing pin of the firearm. This condition is known as cook This is known as an interrupted lug-bolt locking system. off and is to be avoided for safety reasons during the use The bolt carrier 24 is slidably supported in the housing of a firearm. or receiver 12 and is reciprocated during operation of the It accordingly is one of the objects of this invention to firearm. The bolt carrier and bolt are reciprocated by a provide an automatic firearm which includes means for rod 26 having a section 28 disposed within the slot 30 reducing the hazards involved when a cook-off condition formed in the bolt carrier 24. The rod is reciprocated by becomes incipient. In carrying this object forward a heat 50 a suitable gas operated piston which is slidable about the sensing device is provided which senses the temperature barrel and urged in one direction by a spring 32. This gas of the firearm and when this temperature reaches a point operating mechanism forms no part of the present inven where cook-off of a cartridge is incipient the heat sensing tion, it being understood however that each time a car device causes the firearm to be automatically switched to tridge is fired the bolt will be moved toward the right to an automatic open-bolt mode of operation. 55 an position, in FIG. 1, against the force of the Another object of this invention is to provide a firearm spring 32 and then returned to a position under which has a fire control system that can be selectively the control of the fire control mechanism to be described. manually set to provide automatic closed-bolt operation, The barrel 14 is provided with a cylindrical bore 34, automatic open-bolt operation and semiautomatic closed one end of which is positioned adjacent the firing cham bolt operation. In addition the firearm can be provided 60 ber 14B and the bore 14A. A piston 36 is reciprocable with means for automatically switching the firearm to an within the bore 34 and has a piston rod 38 attached automatic open-bolt operation when the temperature of thereto which is formed with a slot 40. The rod 38 passes the firearm reaches a point where cook-off of a cartridge through an insert 42 and a chamber 44 is defined by the is incipient and regardless of the manual setting of the end of the piston and a part of the bore 34. The chamber firearm. 65 44 is filled with a material which expands with increas In the drawings: ing temperature, for example mercury. It is to be under 'FIG. is a view partly in section of a firearm which has stood however, that chamber 44 could contain any other a fire control system made in accordance with this in type of material which expands with increasing tempera vention; ture and which is capable of forcing the piston 36 down FIG. 2 is a view partly in section of a part of the fire 70 wardly or out of the bore 34, in FIG. 1, when the barrel arm shown in FIG. 1 and illustrating a fire control cam in of the rifle increases its temperature. Thus, an axially 3,618,455 3 4 expandable bimetal would be suitable for forcing the pin 84 is rotatably supported by the housing 16 and is piston out of the chamber in response to the tempera connected with a mode selector knob designated by ref ture of the barrel. It will, of course, be appreciated that erence numeral 86 and illustrated in FIG. 1. The mode barrel temperature will depend upon the rate of firing Selector knob 86 can be manually adjusted by the opera of the firearm and, as will be described hereinafter, the tor of the firearm to provide automatic open-bolt opera movement of the piston, in response to a temperature tion, automatic closed-bolt operation and semiautomatic condition of the barrel, results in actuating the fire con closed-bolt operation since rotation of the selector knob trol mechanism so that the firearm is switched to the auto 86 rotates the cam pin 84 provided with the cam sur matic open-bolt mode. Where an expandable fluid is used face 84A. to actuate piston 36 a spring (not illustrated) is provided FIG. 2 illustrates the cam pin or rod 84 in such a for urging the piston against the fluid. O position as to provide automatic closed-bolt operation for A fire control operating rod 48 is provided which the firearm. It will be observed that in this position of passes through the opening 40 in the piston rod 38. The the cam pin 84 the full diameter of the pin is disposed rod also passes through an opening formed in a support between the arms 66A and 72B of the bolt carrier sear section 50 of the barrel 14 and this rod has a spring re 66 and the hammer sear 72. The end 66B of the bolt tainer 52. A spring 54 is disposed between the part 50 5 carrier Sear is now moved clockwise, from its position and the part 52 and constantly urges or forces the rod shown in FIG. 3, so that it cannot engage a sear abut 48 toward the left in FIG. 1. The rod 48 carries a pawl ment wall 24A formed in the bolt carrier 24. This should 48A which, in the position shown in FIG. 1, engages a be contrasted to the FIG. 3 position of the bolt carrier part of the piston rod 38 to prevent the spring 54 from Sear 66 where the end 66B has engaged the wall 24A pushing the rod toward the left as viewed in FIG. 1. It 20 formed on the bolt carrier 24 to hold the bolt carrier in will be appreciated, however, that as the fluid in chamber an open-bolt position. With the parts, as illustrated in 44 expands the piston 36 and rod 38 are moved toward FIG. 2, the bolt is projected forward and a wall or sear the insert 42 and when the piston becomes engaged with abutment 24B formed in the bolt carrier 24 will engage the insert 42 the pawl 48A will be released since it can the disconnector sear 80 to pivot it counterclockwise in slide through the opening 40 formed in the piston rod FIG. 2. This will cause the abutment wall 80A of the 38. The spring 54 will now move the rod 48 to the left disconnector sear 80 to become disengaged from the and to a position where the pawl 48A engages the barrel Sear abutment 74B on the hammer 74 with the result extension part 50. As will be described this will cause the that after the bolt is closed and locked the hammer 74 is fire control mechanism to be switched to the automatic released and will move forward striking the firing pin open-bolt mode of operation. 30 22A to fire a cartridge. This of course assumes that the FIGS. 2, 3 and 4 illustrate the fire control parts of trigger 18 has been pulled counterclockwise in FIG. 2 this invention and as will become apparent hereinafter So that sear wall 18A is out of the way or disengaged the fire control mechanism can be set to provide auto from Sear abutment 74C formed on hammer 74. After matic closed-bolt operation as shown in FIG. 2, automatic the cartridge is fired the bolt carrier 24 is moved toward open-bolt operation as shown in FIG. 3 and semiauto 35 the open bolt position by the gas operating mechanism matic closed-bolt operation as shown in FIG. 4. The term and as long as the trigger 18 is pulled to disengage sear closed bolt operation, as used herein, means that the boit abutment 18A from sear abutment 74C the firearm will is returned to a closed position when the trigger is re be continuously fired due to continuous reciprocation of leased. The term open-bolt operation as used herein 40 the bolt 24. In this regard each time the bolt is moved means that the bolt is set to an open bolt position when to the open bolt position the bolt carrier engages the ever the trigger is released. It will of course be appre hammer 74 to pivot it to a position where it is seared ciated that as the bolt moves toward a closed position by Sear 80. When the trigger is finally released the bolt it forces a cartridge into the firing chamber from a maga will end up in the closed position shown in FIG. 2 and zine which is not illustrated and during the closed-bolt the hammer will be seared by the trigger. mode operation the cartridge is forced into the firing 45 If the cam selector pin 84 is moved to the automatic chamber and the bolt closed when the trigger is released. open-bolt position, as shown in FIG. 3, the portion 66A For open bolt operation the bolt is seared in a retracted of the bolt carrier sear 66 engages the flat wall 84A of the position and no cartridge is fed into the firing chamber can rod or pin 84. This permits the part 66A to move closer to part 72B of sear 72 and in effect permits a coun after the trigger is released. 50 terclockwise rotation of sear 66 under the influence of Referring now to FIGS. 2-4 it is seen that the hous Spring 68. Now as the bolt carrier 24 is moved to an ing 16 supports pivot pins 60, 62 and 64 which are suit open bolt position by the gas operating mechanism the ably supported by the housing 16. The pin 60 pivotally end 66B of Sear 66 engages the sear abutment 24A of the Supports a bolt carrier Sear designated by reference bolt carrier to hold the bolt carrier in the open bolt posi numeral 66. This sear is urged in a counterclockwise 55 tion. This of course is assuming that the trigger 18 has direction by a spring 68 which engages the sear 66 and been released so that the sear abutment wall 18A of the the housing or some part fixed to the housing to urge trigger engages the Sear abutment wall 74C provided by a the Sear 66 counterclockwise. The trigger 18 is pivotally notch formed in the hammer 74. It thus will be apparent supported by pin 62 and is urged toward the dotted line from an inspection of FIG. 3 that once the trigger 18 is released position shown in FIG. 4 by a spring 70. The 60 released and the selector knob 86 in the automatic open pin 62 also rotatably supports a hammer sear 72 which bolt mode of operation the bolt carrier 24 will be held in is urged in a counterclockwise direction as viewed in FIG. the open bolt position once the trigger is released. When 2 by a spring 73 located between trigger 18 and sear 72. the trigger is pulled the part 18B of the trigger causes The sear 72 has a projecting abutment portion 72A which, the part 66A and the sear 66 to rotate clockwise in FIG. at times, engages the abutment or wall 74A provided by a 65 3 thereby releasing 66B from 24A and permitting the slot formed in a hammer 74. The hammer 74 is pivotally bolt carrier 24 to continuously reciprocate as long as the supported by a pin 76 and is urged in a counterclockwise trigger is pulled. During the automatic open-bolt mode of direction toward the firing pin head 22A by a spring 78. operation, as shown in FIG. 3, the wall 24B on the bolt In addition to the fire control parts which have been also moves the disconnector sear 80 counterclockwise, as described a disconnector sear 80 is provided which is 70 shown in FIG. 2, to release the hammer 74 after the bolt pivotally supported by rod or pin 64 and which is urged is closed and locked. Sear abutment walls 18A and 74C in a clockwise direction, in FIG. 2, by a spring 82. are of course disengaged as long as the trigger is pulled The fire control mechanism shown in FIGS. 2 through clockwise in FIG, 3. 4 further includes a rotatable cam pin or rod 84 having Referring now more particularly to FIG. 4 the cam pin a cylindrical shape and a flat cam or wall 84A. The cam 75 84 is now illustrated in such a position as to provide a 3,618,455 5 6 semiautomatic closed-bolt mode of operation. In FIG. 4 when said bolt is shifted to an open position and when the cam wall 84A now engages the part 72B of sear 72 said trigger is released, a manually operable mode selec while the cylindrical portion of the cam engages part 66A tor cam for adjusting the position of said bolt sear where of sear 66. It can be seen that with this position of the can by said bolt sear can be pivoted out of a path traversed pin the part 72B has moved counterclockwise from its by said bolt sear abutment means whereby said bolt can position in FIG. 3 under the influence of a spring 73 and be moved to a closed position to provide a closed-bolt now the sear part 72A can engage the sear wall 74A of mode of operation for said firearm, said selector cam be the hammer to hold the hammer in the position shown ing shiftable to a position where it permits said bolt sear to in FIG. 4 when the hammer is moved to this position by move to a position where it can engage said bolt sear abut the bolt carrier 24. It will be further observed that the part 10 ment means to provide an open-bolt mode of operation, a 66B of sear 66 is in such a position that it cannot engage hammer for said firearm, said hammer cooperating with a sear wall 24A and therefore the bolt will be moved to a firing pin carried by said bolt, sear surfaces located re closed position without impediment by sear 66. When the spectively on said hammer and said trigger for controlling bolt moves to a closed position it moves the Sear 80 to the of said hammer, a heat sensing means in said provide a partial release of hammer 74 and the hammer 5 barrel which is actuated whenever the temperature of said will be fully released when the trigger is pulled to dis barrel reaches a point where cook-off of a cartridge is engage sear walls 18A and 74C. When the trigger 18 is incipient, and means operated in response to the actuation released (dotted line position) in FIG. 4 the part 72C of of said heat sensing means for rotating said mode selec sear 72 engages the trigger 18 so as the trigger moves tor cam to a position wherein said bolt carrier sear is to the released position it moves sear 72 with it causing 20 positioned to engage said bolt to provide for open-bolt 72A to become disengaged from sear abutment 74A but operation of said firearm. also causing sear abutment 18A on the trigger to engage 2. A fire control mechanism for a firearm comprising, sear abutment 74C on the hammer. This holds the a firearm having a reciprocable bolt carrier suppotring a hammer retracted until the trigger is pulled. bolt, first and second bolt sear abutments on said bolt The firearm of this invention will be automatically 25 carrier, a pivotally mounted hammer, a pivotally mounted switched to the automatic open-bolt mode of operation disconnector sear having a sear abutment engageable with (FIG. 3) whenever the temperature, as sensed by the fluid a first sear abutment formed on said hammer and en in chamber 44, reaches a point where cook-off of a car gageable with said first bolt sear abutment on said bolt tridge is incipient. As previously pointed out when this carrier to release said hammer from said disconnector dangerous temperature exists the rod 48 is released and 30 sear when said bolt moves to a closed position, a piovtal is moved leftwardly in FIG. 1 by the spring 54. It is seen ly mounted bolt carrier sear engageable with said second in FIG. 1 that the rod 48 is connected with a bracket 90 sear abutment on said bolt carrier when said bolt carrier which in turn is connected with a length of wire 92 which sear is pivoted into the path of movement of said second is secured to and loosely wrapped around a portion of the sear abutment, a pivotally mounted hammer sear, said cam pin 84 to permit adjustment of knob 86 and pin 84. 35 hammer sear having a part engageable at times with a If desired tape could be used instead of wire or any other second abutment on said hammer, a trigger, said trigger device which is capable of rotating the cam pin 84 to its having a trigger abutment engageable with a third abut FIG. 3 position whenever the rod 48 is released by the ment on said hammer, a manually operable rotatable se heat sensor. It therefore will be appreciated that should lector cam positioned between and in engagement with the temperature of the barrel reach a condition where 40 said hammer sear and said bolt carrier sear, said selector cook-off of a cartridge is incipient the pawl 48A is re cam in a first position permitting said bolt carrier sear to leased and the spring 54, through the linkage, consisting pivot to a position where it can engage said second sear of the rod 48 and the wire 92, moves the selector cam abutment on said bolt carrier while maintaining said pin 84 to the FIG.3 position which provides the automatic hammer sear out of engagement with said second abut open-bolt mode of operation if the selector cam is not 45 ment on said hammer to provide automatic open-bolt already in this position. In such a position the Selector operation, said selector cam in a second position causing knob 86 is of course moved with the cam pin 84 and any said bolt carrier sear to assume a position where it is dis attempt by the operator to shift the gun to the automatic engaged from said second bolt sear abutment and causing closed-bolt or semiautomatic closed position will have no said hammer sear to be disengaged from said hammer to effect since once the selector knob 86 is released by the 50 provide automatic closed-bolt operation, said selector cam operator spring 54 will immediately switch the firearm to in a third position permitting said hammer sear to engage the automatic open-bolt mode of operation. said hammer while maintaining said bolt carrier sear out It is pointed out that in the FIGS. 2 and 3 positions of of the path of movement of said second sear abutment on the selector cam pin 84 the sear part 72A cannot become said bolt carrier to provide semiautomatic closed-bolt engaged with sear abutment wall 74A on the hammer 74 operation, shiftable means connected to said selector cam, as the trigger is pulled because the cam 84 is positioned a spring for urging said shiftable means in a direction to to prevent this. move said selector cam to said second position to provide It will be apparent to those skilled in the art that it is automatic open-bolt operation, detent means engagable desirable for safety reasons to provide the system that has with said shiftable means to maintain it in one position, been described in order that there will not be a cartridge 60 and heat sensor means associated with said firearm and in the weapon when the bolt is closed which might in operable to release said detent means from said shiftable advertently fire due to the barrel reaching the cook-off means when the temperature of said firearm reaches a temperature point. predetermined value whereby said spring moves said se It should be pointed out that when the heat sensor does lector cam to said automatic open-bolt mode of operation. shift the firearm to the automatic open-bolt mode of Op 65 3. A fire control mechanism for a firearm comprising, eration it is still possible to continuously fire the weapon a barrel having a chamber, a reciprocable bolt including as long as the trigger is pulled. means for closing said chamber and including a bolt What is claimed is: Sear abutment means movable along a predetermined 1. A fire control system for a firearm comprising, a path, a rotatable hammer engageable with a firing pin car firearm having a barrel provided with a firing chamber and 70 ried by said bolt and movable to a cocked position by a reciprocable bolt movable between open and closed said bolt when said bolt is opened, a pivotally mounted positions, a trigger, a pivotally mounted bolt Sear engage bolt sear including means engageable with said bolt sear able with bolt sear abutment means and with said trigger abutment means for holding said bolt in an open bolt and movable at times into engagement with said Sear position whenever said bolt sear is pivoted to a prede abutment means to hold said bolt in an open position termined position, a pivotally mounted hammer sear in 3,618,455 7 8 cluding means engageable with a part of said hammer for said trigger is pulled, said hammer sear being moved out holding said hammer in a retracted position, a trigger, a of engagement with said hammer and said cooperating spring interposed between said trigger and hammer sear, sear surfaces on said hammer and trigger becoming en said trigger and hammer having cooperating engageable gaged when said trigger is released, and means for shift sear surfaces which become engaged whenever said bolt ing said cam means to said second position to provide is retracted and when said trigger is in a released posi automatic open-bolt operation whenever the temperature tion, a pivotally mounted disconnector sear, said discon of the barrel of said fire arm reaches a predetermined nector sear and hammer having engageable sear surfaces value. which become engaged when said bolt is retracted, said References Cited bolt including means engaging said disconnector sear to 0 UNITED STATES PATENTS pivot it in one direction to thereby disengage said hammer 2,714,334 8/1955 Harvey ------89. 49 X and disconnector sear surfaces whenever said bolt is 2,858,741 11/1958 Simpson ------89-40 moved to a closed position, a manually operable mode se 3,045,555 7/1962 Stoner ------89-142 lector cam means located between and engageable with 3,446,114 5/1969 Ketterer ------89-140 said bolt Sear and said hammer sear, said cam means in a 15 first position providing automatic closed-bolt operation FOREIGN PATENTS by maintaining said bolt sear and said hammer sear in predetermined positions, said cam means in a second posi 710,250 6/1954 Great Britain ------89-132 tion providing automatic open-bolt operation by causing BENJAMIN A. BORCHELT, Primary Examiner said bolt Sear to be pivoted into the path of said bolt 20 Sear abutment means on said bolt, said cam means in a S. C. BENTLEY, Assistant Examiner third position maintaining said bolt sear in a position where it cannot engage said bolt abutment means but per U.S. Cl. X.R. mitting Said hammer sear to engage said hammer when 89-14A, 140, 141, 142, 143, 149