A bolt is a mechanical part of a firearm

Firearm

A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...

 that blocks the rear of the chamber

Chamber (weaponry)

In firearms, the chamber is that portion of the barrel or firing cylinder in which the cartridge is inserted prior to being fired. Rifles and pistols generally have a single chamber in their barrels, while revolvers have multiple chambers in their cylinders and no chamber in their barrel...

 while the propellant burns.

In manually-operated firearms, such as bolt-action

Bolt-action

Bolt action is a type of firearm action in which the weapon's bolt is operated manually by the opening and closing of the breech with a small handle, most commonly placed on the right-hand side of the weapon...

, lever-action

Lever-action

Lever-action is a type of firearm action which uses a lever located around the trigger guard area, to load fresh cartridges into the chamber of the barrel when the lever is worked. Most lever-action firearms are rifles, but lever-action shotguns and a few pistols have also been made...

, and pump-action

Pump-action

A pump-action rifle or shotgun is one in which the handgrip can be pumped back and forth in order to eject a spent round of ammunition and to chamber a fresh one. It is much faster than a bolt-action and somewhat faster than a lever-action, as it does not require the trigger hand to be removed from...

 rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas forward.

In an automatic

Automatic firearm

An automatic firearm is a firearm that loads another round mechanically after the first round has been fired.The term can be used to refer to semi-automatic firearms, which fire one shot per single pull of the trigger , or fully automatic firearms, which will continue to load and fire ammunition...

 or semi-automatic firearm

Semi-automatic firearm

A semi-automatic, or self-loading firearm is a weapon which performs all steps necessary to prepare the weapon to fire again after firing—assuming cartridges remain in the weapon's feed device or magazine...

, 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

Extractor (firearms)

An extractor is a part in a firearm that serves to remove brass cases of fired ammunition after the ammunition has been fired. When the gun's action cycles, the extractor lifts or removes the spent brass casing from the firing chamber.-Overview:...

 pulls the spent casing from the chamber. When it moves forward, it strips a cartridge from the magazine

Magazine (firearm)

A magazine is an ammunition storage and feeding device within or attached to a repeating firearm. Magazines may be integral to the firearm or removable . The magazine functions by moving the cartridges stored in the magazine into a position where they may be loaded into the chamber by the action...

 and pushes it into the chamber. Once the case is clear of the chamber, the ejector kicks the case out of the weapon. The extractor and firing pin

Firing pin

A firing pin or striker is part of the firing mechanism used in a firearm or explosive device e.g. an M14 landmine or bomb fuze. Firing pins may take many forms, though the types used in landmines, bombs, grenade fuzes or other single-use devices generally have a sharpened point...

 are often integral parts of the bolt. The slide

Pistol slide

The slide is the part of the weapon on a majority of semi-automatic pistols that moves during the operating cycle and generally houses the firing pin or striker and the extractor, and serves as the bolt...

 of a semi-automatic pistol

Pistol

When distinguished as a subset of handguns, a pistol is a handgun with a chamber that is integral with the barrel, as opposed to a revolver, wherein the chamber is separate from the barrel as a revolving cylinder. Typically, pistols have an effective range of about 100 feet.-History:The pistol...

 is a form of bolt.

See also

• Breechblock
  Breechblock
  A breechblock is the part of the firearm action that closes the breech of a weapon at the moment of firing....
  
  
• Open bolt
  Open bolt
  A semi or full automatic firearm is said to fire from an open bolt if, when ready to fire, the bolt and working parts are held to the rear. When the trigger is pulled the bolt goes forward, feeding a round from the magazine into the chamber and firing it...
  
  
• Closed bolt
  Closed bolt
  A semi or full-automatic firearm which is said to fire from a closed bolt is one where, when ready to fire, a round is in the chamber and the bolt and working parts are forward...
  
  
• Recoil operation
  Recoil operation
  Recoil operation is an operating mechanism used in locked-breech, autoloading firearms. As the name implies, these actions use the force of recoil to provide energy to cycle the action...
  
  
• Blowback (arms)
  Blowback (arms)
  Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the propellant charge....
  
  
• Gas-operated reloading
  Gas-operated reloading
  Gas-operation is a system of operation used to provide energy to operate autoloading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed...
  
  
• Slamfire
  Slamfire
  A slamfire is a premature, unintended discharge of a firearm that occurs as a round is being loaded into the chamber. Slamfires are most common in military firearms that have a free-floating firing pin, as opposed to a spring-loaded one...