Bolt Action | Breech Mechanism - Encyclopedia Britannica

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bolt action, type of breech mechanism that was the key to the development of the truly effective repeating rifle. The mechanism combines the firing pin, a spring, and an extractor, all housed in a locking breechblock. The spring-loaded firing pin slides back and forth inside the bolt, which itself is the breechblock. The bolt is moved back and forth, and partially rotated, in the receiver by a projecting handle with a round knob. One or more lugs at the front or rear of the bolt (or at both) fit into slots in the receiver and lock the bolt firmly in place against the base of the cartridge chamber when the rifle is to be fired. As the bolt is thrust forward, it pushes a cartridge into the chamber and cocks the piece. The trigger releases the spring-driven firing pin inside the bolt. After firing, the extractor on the head of the bolt removes the spent cartridge and ejects it. The bolt moves a new cartridge from the magazine and repeats the process.

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Some bolt actions lock without rotating. Straight-pull bolts are used in the Canadian Ross, the Austrian Mannlicher, and the Swiss Schmidt-Rubin rifles. Bolts that turn to lock have been standard in the Krag-Jorgensen, Lee-Enfield, Springfield, and Lebel rifles, among others.