A system of automatic or semiautomatic firing wherein the bolt remains in the rearward position after each shot or when firing is stopped. Generally weapons of this system have a fixed firing pin. Theoretically, the open bolt system allows for greater cooling to prevent cookoff and a simplified action (e.g., Thompson, Ingram/MAC M-10, and US M3 sub-machineguns). The Winchester Model 55, 22 caliber single shot rifle also fires from an open bolt. Also known as open-breech action.
1