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 that blocks the rear opening (breech) of the barrel

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 delib ...

while the propellant burns, and moves back and forward to facilitate loading/unloading of

cartridge Cartridge may refer to: Objects * Cartridge (firearms), a type of modern ammunition * ROM cartridge, a removable component in an electronic device * Cartridge (respirator), a type of filter used in respirators Other uses * Cartridge (surname), a ...

s from the magazine. The

firing pin A firing pin or striker is a part of the firing mechanism of a firearm that impacts the primer in the base of a cartridge and causes it to fire. In firearms terminology, a striker is a particular type of firing pin where a compressed spring ...

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 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 gas created by the ignition of the propellant charge. Several blowback systems exist wi ...

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 Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge indirectly (through the barrel, through a gas block, and then through a gas tube) into the bolt carrier or slide assembly to cycle the action. F ...

) or a piston system. The

slide Slide or Slides may refer to: Places * Slide, California, former name of Fortuna, California Arts, entertainment, and media Music Albums * ''Slide'' (Lisa Germano album), 1998 * ''Slide'' (George Clanton album), 2018 *''Slide'', by Patrick Glees ...

of a self-loading pistol 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-action ...

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 coc ...

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 A semi-automatic firearm, also called a self-loading or autoloading firearm (fully automatic and selective fire firearms are also variations on self-loading firearms), is a repeating firearm whose action mechanism ''automatically'' loads a follo ...

( 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) Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...

. 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 magazine and pushes it into the chamber. A

telescoping bolt A telescoping bolt (also known as an overhung bolt) is a firearm bolt which telescopes over, that is, wraps around and past, the breech end of the barrel. This feature reduces the required length of a weapon such as a submachine gun significant ...

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 Rotating bolt is a method of locking the breech (or rear barrel) of a firearm closed for firing. Johann Nicolaus von Dreyse developed the first rotating bolt firearm, the " Dreyse needle gun", in 1836. The Dreyse locked using the bolt handle ...

, 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 In firearms operating systems, the term roller locked refers to locking the bolt with rollers. Notable examples of firearms using this method are the MG 42 general-purpose machine gun, and the CZ 52 semi-automatic pistol. It was also applied in t ...

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 bolt ...

or Anschütz 1827 Fortner (both straight-pull rifles).

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 Corporatio ...

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 The Karabiner Modell 1931 (K. 31/Kar. 31/Mq. 31) is a magazine-fed, straight-pull bolt-action rifle. It was the standard issue rifle of the Swiss armed forces from 1933 until 1958 though examples remained in service into the 1970s. It has a 6-ro ...

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