Bolt from a Karabiner 98k bolt-action rifle. Note the curved handle on the side for manual operation">bolt-action.html" ;"title="Karabiner 98k bolt-action">Karabiner 98k bolt-action rifle. Note the curved handle on the side for manual operation thumb"> thumb"> thumb"> Slide locked back on a Desert Eagle pistol, showing the gas-operated rotating bolt mechanism A bolt is the part of a repeating,

breechloading A breechloader is a firearm in which the user loads the ammunition from the breech end of the barrel (i.e., from the rearward, open end of the gun's barrel), as opposed to a muzzleloader, in which the user loads the ammunition from the ( muzzle ...

firearm A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions). The first firearms originate ...

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 stave (wood), staves and bound by wooden or metal hoops. The word vat is often used for large containers ...

chamber 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 another motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicle ...

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

magazine A magazine is a periodical literature, periodical publication, print or digital, produced on a regular schedule, that contains any of a variety of subject-oriented textual and visual content (media), content forms. Magazines are generally fin ...

. 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 sprin ...

and extractor are often integral parts of the bolt. The terms "

breechblock A breechblock (or breech block) is the part of the firearm action that closes the breech of a breech loading weapon (whether small arms or artillery) before or at the moment of firing. It seals the breech and contains the pressure generated by ...

" 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, for according to Newton's third law the force requ ...

, or

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 gas piston (short-stroke or long-stroke piston) system. The slide of a self-loading pistol contains the same components and serves similar functions.

Operation

In manually operated firearms, such as

bolt-action Bolt action is a type of manual Action (firearms), firearm action that is operated by ''directly'' manipulating the bolt (firearms), turn-bolt via a cocking handle, bolt handle, most commonly placed on the right-hand side of the firearm (a ...

lever-action The toggle-link action used in the iconic Winchester Model 1873 rifle, one of the most famous lever-action firearms Picture showing a Volcanic Pistol A lever action is a type of action for repeating firearms that uses a manually operated cocki ...

, and

pump-action Pump action is a type of manual firearm action that is operated by moving a sliding handguard on the gun's forestock. When shooting, the sliding forend is pulled rearward to eject any expended cartridge (firearms), cartridge and typically to co ...

rifle A rifle is a long gun, long-barreled firearm designed for accurate shooting and higher stopping power, with a gun barrel, barrel that has a helical or spiralling pattern of grooves (rifling) cut into the bore wall. In keeping with their focus o ...

s or

shotgun A shotgun (also known as a scattergun, peppergun, or historically as a fowling piece) is a long gun, long-barreled firearm designed to shoot a straight-walled cartridge (firearms), cartridge known as a shotshell, which discharges numerous small ...

s, 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, burst fire, or fully automatic), 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 th ...

) or the expanding gas ( blowback and

) and forward by a spring. 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 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 significan ...

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 and unlock. This is most commonly found in bolt-action firearms but is also found in 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 ra ...

, 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 or

Anschütz 1827 Fortner Anschütz 1827 Fortner is a straight pull rifles, straight-pull action biathlon rifle designed by Peter Fortner junior and produced in cooperation with J. G. Anschütz. The rifle has been dominant in the sport of biathlon since the late 1980s, ...

(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.

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)

Operation

Closed bolt vs. open bolt

See also

References