Rotating bolt
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Rotating bolt is a method of locking found in gas operated, semi-automatic or selective fire firearms — such as the M1, M14, M16, the L85A1/A2 and the AK-47/74 — in which the bolt, upon contact with the breech, rotates and locks into place, being held in place by lugs attached to the breech or barrel extension.
Upon closing, the bolt passes through the slots cut in the front of the barrel extension, and then rotates; at this point it is locked in place. The bolt remains locked until the action is cycled, either manually by the operator, or mechanically by the gas created by discharging the rifle pushing on the operating rod or bolt carrier, which then rotates the bolt and unlocks it from the breech so that it can be withdrawn in order to extract and eject the spent casing, and chamber a new round.
The gas port, which meters a portion of the combustion gases into the action in order to cycle the weapon, is typically located either midway down the barrel or near the muzzle of the weapon. In this way it functions as a delay, ensuring that the bolt remains locked until chamber pressure has subsided to a safe level.
Rotating bolts are not exclusive to gas-operated weapons; they are also found in some lever-action and pump-action designs.
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