Rotating bolt
A firearm breech mechanism in which the bolt rotates to lock into the receiver or barrel extension and rotates again to unlock for cycling.
Bolt-action firearm: A firearm whose action is operated by manually moving a bolt to load, fire, extract, and eject cartridges. Many bolt-action rifles use a rotating bolt to lock the breech.
Cartridge (firearms): A complete firearm ammunition unit containing a projectile, propellant, primer, and case. The bolt closes behind the cartridge and supports its case during firing.
M16 rifle: A family of military rifles developed in the United States, using a rotating bolt and gas-operated action. Its bolt rotates into a barrel extension, a widely studied implementation.
Tilting bolt: A breech mechanism in which a bolt tilts to engage or disengage locking surfaces. It locks by changing angle rather than rotating about the bolt’s axis.
Self-loading firearm: A firearm that uses energy from firing or another power source to load its next cartridge automatically. Rotating bolts are common in self-loading rifles and machine guns.
Bolt carrier: A moving assembly that houses or guides a firearm bolt and transmits operating motion to it. In many self-loading firearms, the carrier moves the bolt through its locking and unlocking cycle.
Chamber (firearms): The part of a firearm that holds a cartridge in position for firing. The rotating bolt locks the cartridge into the chamber’s breech end.
AK-47: A Soviet assault rifle designed by Mikhail Kalashnikov and adopted in 1949, with a rotating bolt. Its two-lug bolt locks by rotating into the receiver’s barrel extension.
Roller-delayed blowback: A firearm operating system that uses rollers to delay breech opening without a rigidly locked bolt. Its rollers delay opening, unlike the rotating bolt’s positive mechanical lock.
Bolt-action rifle: A rifle whose cartridges are cycled by manually operating a bolt between shots. The rotating bolt provides a strong, mechanically simple lock in many such rifles.