The bolt assembly is the heart of a firearm's operating mechanism. It locks into the barrel extension to seal the chamber during firing, contains the firing pin that strikes the primer, and houses the extractor that pulls spent casings from the chamber. In semi-automatic rifles like the Winchester Model 100, the bolt is driven by a gas-operated system that harnesses propellant gases to cycle the action automatically. A complete bolt assembly typically includes the bolt body, firing pin, firing pin spring, extractor, extractor spring, ejector, and associated pins and plungers.
