Thursday, October 12, 2017

SECTION IV: FUNCTIONING


  •  11. ACTION OF TRIGGER AND SEAR IN FIRING.—Downward pressure on the trigger crank lever causes a rearward mo tion of the trigger crank. The lower arm of the sear is in contact with the trigger crank, hence moves rearward with it. The sear being pivoted near its upper portion, this rearward movement of the lower arm forces the sear head down out of contact with the cocking notch of the striker. This down ward movement also compresses the sear spring. Pressure on the trigger crank lever should be released when the gun fires. 
  •  12. ACTION OF FIRING MECHANISM.—The firing mechanism consists of the striker spring, striker, rocker plunger, rocker and rocker pin, firing pin, and firing-pin spring. The firing mechanism operates when the striker is released by the sear head. The compressed striker spring drives the striker to the rear about 1 inch where it delivers a sharp blow against the rocker plunger, the force of which is transmitted to the rocker and through the rocker to the firing pin. The firing pin is driven forward compressing the firing-pin spring, and striking and igniting the primer of the cartridge. 
  • 13. ACTION OF SAFETY BOLT.—The safety bolt seated in a bracket on the left side of the breech ring engages the lower arm of the sear. The breechblock cap contacts the rear end of the safety bolt and is notched to permit the safety bolt to move to the rear when the breech is completely closed. The firing pin is eccentrically mounted to permit it to be brought in line with the primer of the cartridge only when the breech is completely closed. Therefore, the sear can re lease the striker to cause discharge only when the breech is completely closed.
  • 14. ACTION IN RECOIL.—a. Action of the powder gases on the breechblock at the moment of discharge causes the recoil of the united barrel and breechblock, driving them rearward a distance of about 8 inches. b. The bronze shoes attached to the barrel slide in the steel guides attached to the cradle, compelling proper direction of recoil. c. The firing-pin spring returns the firing pin, rocker, and rocker plunger to position when the rocker plunger moves to the rear away from the striker. d. The sear, a recoiling part, moves away from the striker, a nonrecoiling part, permitting the sear head under the action of the sear spring to rise behind the cocking notch of the striker. e. Recoil is resisted, its speed regulated, and movement stopped by action of the recoil mechanism which is attached to the recoiling parts by the piston cross head key. Two forces resist the movement: The strong counterrecoil spring is compressed, and the movement of the piston head is re sisted by the oil in the cradle. The oil follows two courses as It flows to the front of the piston head: (1) It passes through the hollow portion of the forward end of the piston rod. (2) It forces the piston valve open against the resistance of the piston-valve spring and flows through the holes in the piston head.
  • 15. ACTION OF CotnsrTERRECoiL.—a. Recoil being stopped, the recoiling parts are instantly moved forward by pressure of the compressed counterrecoil spring against the piston head. ft. The piston valve actuated by the piston-valve spring closes the holes in the piston head just before counterrecoil starts. Therefore the speed of counterrecoil is regulated by the rate at which the oil in the cradle flows through the hollow portion of the forward end of the piston rod. c. The final movement of the returning parts is gradually stopped and shock to the gun prevented by the action of the counterrecoil buffer which progressively closes the hollow portion of the piston rod through which the oil must flow. d. As the recoiling parts return to battery the sear carries the striker forward, compresses the striker spring, and auto matically cocks the gun. To permit this action to occur the thumb must be removed from the trigger crank lever as the gun fires.
  • 16. EXTRACTION AND EJECTION OF CARTRIDGE CASE.—The ex tractor seated in the breech ring is pivoted near its lower end on the extractor pin. When the breech is opened by ro tating the breechblock smartly to the left, the extractor cam on the face of the breechblock strikes the heel of the ex tractor, depresses it, and causes the upper arm of the extractor to rotate to the rear. The upper arm of the extractor engaged in front of the rim of the cartridge case extracts the empty case and ejects it from the gun.

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