Rotating bolt

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M16 bolt locking fig 2-6.png
M16 bolt locking
M16 bolt unlocking fig 2-8.png
M16 bolt unlocking
Rotating Bolt.png

Rotating bolt is a method of locking used in firearms. Johann Nicolaus von Dreyse developed first rotating bolt the "Dreyse needle gun" in 1836. The Dreyse locked using the bolt handle rather than lugs on the bolt head like Mauser M 98 or M16. The first rotating bolt rifle with two lugs on the bolt head was the Lebel Model 1886 rifle.

Ferdinand Ritter von Mannlicher, who had earlier developed non-rotating bolt straight-pull rifle, developed the Steyr-Mannlicher M1895, a straight-pull rifle with rotating bolt, which was issued to the Austro-Hungarian Army. Mannlicher then developed the Mannlicher 1900 rifle which had a rotating bolt and was operated by a gas piston. This was an inspiration for later 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on the operating rod or bolt carrier, which then rotates the bolt and unlocks it from the breech so that it can be withdrawn in order to extract and eject the spent casing, and chamber a new round.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 found in gas-operated, recoil-operated, bolt action, lever-action and pump-action weapon designs. Another form of delayed blowback which the bolt head rotates as the firing pin strikes locking the chamber until the gas pressure reaches a safe level to extract. As the firing pin retracts, the bolt head turns anti-clockwise unlocking the breech.

Examples of Rotating bolt firearms[edit]

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