A semi or full-automatic

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 ...

which is said to fire from a closed bolt or closed breech is one where, when ready to fire, a round is in the chamber and the bolt and working parts are forward ''in battery''. When the trigger is pulled, the firing pin or striker fires the round; the action is cycled by the energy of the shot, sending the bolt to the rear, which extracts and ejects the empty

cartridge case A cartridge, also known as a round, is a type of pre-assembled firearm ammunition packaging a projectile (bullet, shot, or slug), a propellant substance ( smokeless powder, black powder substitute, or black powder) and an ignition device ( pr ...

; and the bolt goes forward, feeding a fresh round 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 ...

into the chamber, ready for the next shot.

World War I aircraft

When

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

era machine guns were being tried for use on aircraft, the Lewis gun was found not to be usable with a gun synchronizer for forward firing through the propeller, due to its firing cycle starting with an

open bolt A firearm is said to fire from an open bolt or open breech if, when ready to fire, the bolt and working parts are held to the rear of the receiver, with no round in the chamber. When the trigger is actuated, the bolt travels forward, feeds a car ...

. Maxim style arms fired with a cycle starting with a closed bolt, and since the bullet firing from the gun started the firing cycle, it was much easier to set the synchronizer to trigger the gun only when the propeller's blade was not directly in front of the gun's muzzle. These included: *

Vickers machine gun The Vickers machine gun or Vickers gun is a Water cooling, water-cooled .303 British (7.7 mm) machine gun produced by Vickers Limited, originally for the British Army. The gun was operated by a three-man crew but typically required more me ...

* Both the rectangular-receiver lMG 08 and lightened-receiver LMG 08/15 Spandau gun, and Parabellum LMG 14 gun * Improvements introduced by Swedish armaments designer Carl Gustave Swebilius to the American

M1895 Colt–Browning machine gun The Colt–Browning M1895, nicknamed "potato digger" because of its unusual operating mechanism, is an air-cooled, belt-fed, gas-operated machine gun that fires from a closed bolt with a cyclic rate of 450 rounds per minute. Based on an 1889 desi ...

for aircraft use, creating the M1917 and M1918 Marlin-Rockwell machine guns for the USAAS

Comparison with open bolt design

A closed bolt design has both advantages and disadvantages when compared to an

design:

Advantages

*More accurate for the first round and for semi-automatic fire: **No movement of heavy working parts prior to firing to potentially inhibit accuracy. **Round sits consistently in the chamber. **Potentially shorter delay between operator pulling the trigger and round being fired (also known as lock time). *Cleaner operation – less potential for dust and other foreign debris to enter the gun, since the action remains closed unless the weapon is firing. *Action can be locked forward to further reduce noise in a suppressed weapon. *Can carry an additional round in the chamber, increasing ammunition capacity by one round beyond the

's maximum limit.

Disadvantages

*More complicated and expensive to manufacture. *Less heat

dissipation In thermodynamics, dissipation is the result of an irreversible process that affects a thermodynamic system. In a dissipative process, energy ( internal, bulk flow kinetic, or system potential) transforms from an initial form to a final form, wh ...

from closed chamber (increased danger of

cooking off Cooking off (or thermally induced firing) is unfired weapon ammunition explosion, exploding prematurely due to heat in the surrounding environment. The term is used both for detonation of ammunition not loaded into a weapon, and unintended firin ...

) *The extra round in the chamber can be a safety hazard, as even when the magazine is removed, the round in the chamber will still be ready to fire, and must be manually ejected.

Uses

Closed-bolt designs are often used in

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. The improved accuracy of closed-bolt weapons is more desirable, while the poorer heat dissipation is less of an issue for slower-firing weapons. In contrast, open-bolt designs are more often used in automatic weapons, such as machine guns. For fast-firing automatic weapons, heat will rapidly build up from sustained firing, but accuracy is of less importance. Thus, the improved heat dissipation of open-bolt designs is generally more desirable in automatic weapons.

Closed-bolt firearms

Examples of closed-bolt firearms include: * AR-15 style rifle * Armalite AR-10 * Armalite AR-16 * Armalite AR-18 * FAMAE SAF * FN F2000 * Heckler & Koch MP5 * Heckler & Koch UMP * Heckler & Koch G3 * Heckler & Koch G36 * Heckler & Koch HK21 * Kalashnikov rifle * Maxim gun * Mendoza HM-3 * MG 08 * MG 13 * MG 17 machine gun * MG 131 machine gun *

M2 Browning machine gun The M2 machine gun or Browning .50-caliber machine gun (informally, "Ma Deuce") is a heavy machine gun that was designed near the end of World War I by John Browning. While similar to Browning's M1919 Browning machine gun, which was chamber ...

M16 rifle The M16 (officially Rifle, Caliber 5.56 mm, M16) is a family of assault rifles adapted from the ArmaLite AR-15 rifle for the United States Armed Forces, United States military. The original M16 was a 5.56×45mm NATO, 5.56×45mm automatic ...

* Parabellum MG14 * SIG 550 * Spectre M4 * Steyr AUG *

Vickers Machine Gun The Vickers machine gun or Vickers gun is a Water cooling, water-cooled .303 British (7.7 mm) machine gun produced by Vickers Limited, originally for the British Army. The gun was operated by a three-man crew but typically required more me ...

Mixed mode firearms

Examples of mixed mode firearms (capable of operating from either an open bolt or closed bolt) include: * ArmaLite AR-100 - AR-101 and AR-102 * CETME Model A *

FG 42 The FG 42 (German language, German: ''Fallschirmjägergewehr'' 42, "paratrooper rifle 42") is a selective fire, selective-fire 7.92×57mm Mauser automatic rifle produced in Nazi Germany during World War II. The weapon was developed specifically ...

* FN SCAR - Heat Adaptive Modular Rifle * LWRC Infantry Automatic Rifle - M6A4 * M1941 Johnson machine gun * Dror light machine gun

References

External links

How Does it Work: Open Bolt vs Closed Bolt Firearms
{{webarchive , url=https://web.archive.org/web/20230410101726/https://www.youtube.com/watch?v=Ga4uoWmfEt4 , date= 2023-04-10 Firearm actions Firearm terminology