A bolt is the part of a repeating,

breechloading A breechloader is a firearm in which the user loads the ammunition ( cartridge or shell) via the rear (breech) end of its barrel, as opposed to a muzzleloader, which loads ammunition via the front ( muzzle). Modern firearms are generally bre ...

firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...

that blocks the rear opening (breech) of the

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, ...

chamber Chamber or the chamber may refer to: In government and organizations *Chamber of commerce, an organization of business owners to promote commercial interests *Legislative chamber, in politics *Debate chamber, the space or room that houses deliber ...

while the

propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the ...

burns, and moves back and forward to facilitate loading/unloading of cartridges from the

magazine A magazine is a periodical publication, generally published on a regular schedule (often weekly or monthly), containing a variety of content. They are generally financed by advertising, purchase price, prepaid subscriptions, or by a combinatio ...

. The firing pin and extractor are often integral parts of the bolt. The terms "breechblock" and "bolt" are often used interchangeably or without a clear distinction, though usually, a bolt is a type of breechblock that has a nominally circular cross-section. In most automatic firearms that use delayed blowback,

recoil Recoil (often called knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged. In technical terms, the recoil is a result of conservation of momentum, as according to Newton's third law the force r ...

gas operation Gas-operation is a system of operation used to provide energy to operate locked breech, autoloading firearms. In gas-operation, a portion of high-pressure gas from the cartridge being fired is used to power a mechanism to dispose of the spent ...

, the bolt itself is housed within the larger bolt carrier group (BCG), which contains additional parts that receives rearward push from a gas tube ( direct impingement) or a

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-t ...

system. The slide of a

self-loading pistol A semi-automatic pistol is a type of repeating single- chamber handgun (pistol) that automatically cycles its action to insert the subsequent cartridge into the chamber (self-loading), but requires manual actuation of the trigger to actua ...

can be considered a bolt carrier, as it contains the same components and serves the same functions.

Description

In manually operated firearms such as

bolt-action Bolt-action is a type of manual firearm action that is operated by ''directly'' manipulating the bolt via a bolt handle, which is most commonly placed on the right-hand side of the weapon (as most users are right-handed). Most bolt-actio ...

lever-action The toggle-link action used in the iconic Winchester Model 1873 rifle, one of the most famous lever-action firearms Lever-action is a type of action for repeating firearms that uses a manually operated cocking handle located around the trigger g ...

, and

pump-action Pump action or slide action is a repeating firearm action that is operated manually by moving a sliding handguard on the gun's forestock. When shooting, the sliding forend is pulled rearward to eject any expended cartridge and typically to co ...

rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas forward. It is manually unlocked and moved to extract the spent casing and chamber another round. In a self-loading firearm ( semi-automatic or

fully-automatic An automatic firearm is an auto-loading firearm that continuously chambers and fires rounds when the trigger mechanism is actuated. The action of an automatic firearm is capable of harvesting the excess energy released from a previous discha ...

), the bolt cycles back and forward between each shot, propelled back by

(

recoil operation Recoil operation is an operating mechanism used to implement locked breech, autoloading firearms. Recoil operated firearms use the energy of recoil to cycle the action, as opposed to gas operation or blowback operation using the pressure of the p ...

) or the expanding gas ( blowback and

) and forward by a

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

. When it moves back, the extractor pulls the spent casing of the previous shot from the chamber, and once the case is clear out of the chamber, the ejector kicks the case out of the firearm. When the bolt moves forward, it picks up a new cartridge from the

and pushes it into the chamber. A telescoping bolt is a bolt that wraps around the breech end of the barrel. This bolt design is often used to reduce overall weapon length without sacrificing barrel length or bolt weight. A turn bolt refers to a firearm component where the whole bolt without using a bolt carrier turns to lock/unlock. This is mostly used to describe manually operated bolt action firearms, but also on some automatic firearms. The most common locking mechanism on rifles is a rotating bolt, which can be classified as a rigid type of bolt lock. Semi-rigid bolt locks have their locking elements movably mounted on either the bolt, barrel or breech housing and using a bolt carrier. Examples of semi-rigid bolt locks are roller-locked bolts, or ball bearings as on

Heym SR 30 The Heym SR 30 is a straight-pull rifle produced in Germany by Heym. The rifle is also available in a left hand version. Locking mechanism The mechanism uses 6 ball bearings symmetrically positioned around the circumference of the bo ...

or Anschütz 1827 Fortner (both

straight-pull rifles Bolt-action is a type of manual firearm action that is operated by ''directly'' manipulating the bolt via a bolt handle, which is most commonly placed on the right-hand side of the weapon (as most users are right-handed). Most bolt-action ...

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.

Gallery

File:Rugersrcarrier.jpg,

AR-15 An AR-15-style rifle is any lightweight semi-automatic rifle based on the Colt AR-15 design. The original ArmaLite AR-15 is a scaled-down derivative of Eugene Stoner's ArmaLite AR-10 design. The then Fairchild Engine and Airplane Corporation ...

bolt carriers File:AK74 bolt.jpg,

AK-74 The AK-74 ( Russian: , tr. ''Avtomat Kalashnikova obraztsa 1974 goda'', lit. 'Kalashnikov assault rifle model 1974) is an assault rifle designed by small arms designer Mikhail Kalashnikov in 1974. While primarily associated with the Soviet ...

bolt and firing pin. File:K31 culasse open.jpg, K31 bolt disassembled File:Desert Eagle beside a box of Speer 325 Grain HP.jpg, Slide locked back on a

Desert Eagle The Desert Eagle is a gas-operated, semi-automatic pistol known for chambering the .50 Action Express, the largest centerfire cartridge of any magazine-fed, self-loading pistol. Magnum Research Inc. (MRI) designed and developed the Desert Eagle ...

pistol, showing the gas-operated rotating bolt mechanism

References

Full Auto
describes the function of the bolt in detail {{Firearms Firearm components bg:Затвор (оръжие) fr:Culasse (arme) it:Otturatore (armi) ru:Затвор (деталь оружия)

Description

Closed bolt vs. open bolt

Gallery

See also

References