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Abolt is the part of arepeating,breechloadingfirearm that blocks the rear opening (breech) of thebarrelchamber while thepropellant burns, and moves back and forward to facilitate loading/unloading ofcartridges from themagazine. Thefiring pin andextractor 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 usedelayed blowback,recoil, orgas operation, the bolt itself is housed within the largerbolt 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. Theslide of aself-loading pistol contains the same components and serves similar functions.
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Inmanually operated firearms, such asbolt-action,lever-action, andpump-actionrifles orshotguns, 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 aself-loading firearm (semi-automatic,burst fire, orfully automatic), the bolt cycles back and forward between each shot, propelled back byrecoil (recoil operation) or the expanding gas (blowback andgas operation) and forward by aspring. When it moves back, theextractor 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 themagazine and pushes it into the chamber.
Atelescoping 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 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 arotating 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.[1] Examples of semi-rigid bolt locks areroller-locked bolts, or ball bearings as onHeym SR 30 orAnschütz 1827 Fortner (bothstraight-pull rifles).
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.
A device/method of holding the bolt open, usually for inspection/reloading/barrel cooling/safety purposes.