Nov. 9, 1971 R. D. PLUMER ET All- 3,618,455 MANUAL OF EN AND CLOSED BOLT WEAPON FIRE CONCROL WITH AUTOMATIC HEAT RESPONSIVE OWERRIDE Filed July 25, 1969 y M & W. W 242 w 2.3227 SEl Of \: - and 2N ( . 22-A-TT T N 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 firearm; 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 rifle 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 automatic firearm 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 chamber 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 cartridge 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 open bolt 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 closed bolt 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.