Bolt (firearms)

Bolt from a Mauser 98 bolt-action rifle. Note the curved handle on the side for manual operation.

A bolt is the part of a repeating, breech-loading firearm that blocks the rear opening (breech) of the barrel chamber while the propellant burns, and moves back and forward to facilitate loading/unloading of cartridges from the magazine. The extractor and firing pin are often integral parts of the bolt.

In gas-operated firearms, the bolt itself is housed within the larger bolt carrier group (BCG), which contains additional parts that receives rearward push from the gas piston.

The slide of a semi-automatic pistol is a form of bolt, as it contains the same parts and serves the same functions.

Description

In manually operated firearms, such as bolt-action, lever-action, and pump-action rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas forward, and is manually withdrawn to chamber another round.

In an automatic or semi-automatic firearm, the bolt cycles back and forward between each shot, propelled by recoil or expanding gas (back) or the recoil spring (forward). When it moves back, the extractor pulls the spent casing from the chamber. When it moves forward, it strips a cartridge from the magazine and pushes it into the chamber. Once the case is clear of the chamber, the ejector kicks the case out of the firearm.

Closed bolt vs. Open bolt

In a closed bolt firearm, the bolt is in its foremost position upon firing. This is opposed to an open bolt firearm where the bolt is held rearward and pulling the trigger releases it to slam forward and fire the cartridge.

See also

References

  • Full Auto describes the function of the bolt in detail
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