A semi or full-automatic firearm 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; and the bolt goes forward, feeding a fresh round from the magazine into the chamber, ready for the next shot.
When World War I 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. 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:
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A closed bolt design has both advantages and disadvantages when compared to an open bolt design:
Closed-bolt designs are often used in rifles. 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.
Examples of closed-bolt firearms include:
Examples of mixed mode firearms (capable of operating from either an open bolt or closed bolt) include:
A machine pistol is a handgun that is capable of fully automatic fire, including stockless handgun-style submachine guns.
A semi-automatic rifle is an auto-loading rifle that fires a single cartridge with each pull of the trigger. It uses part of the fired cartridge's energy to eject the case and automatically loads another cartridge into its chamber. This is in contrast to bolt-action or lever-action rifles, which will require the user to manually chamber a new round before they can fire again, and fully automatic rifles, which fire continuously while the trigger is held down.
A squad automatic weapon (SAW), also known as a section automatic weapon or light support weapon (LSW), is a man-portable automatic firearm attached to infantry squads or sections as a source of rapid direct firepower. Weapons fulfilling this role can be light machine guns, or modified selective-fire rifles fitted with a heavier barrel, bipod and a belt/drum-fed design.
The Colt AR-15 is a product line of magazine-fed, gas-operated, autoloading rifle manufactured by Colt's Manufacturing Company ("Colt") in many configurations. The rifle is a derivative of its predecessor, the lightweight ArmaLite AR-15, an automatic rifle designed by Eugene Stoner and other engineers at ArmaLite in 1956.
The Heckler & Koch G11 is a non-production prototype assault rifle developed from the late 1960s to the 1980s by Gesellschaft für Hülsenlose Gewehrsysteme (GSHG), a conglomeration of companies headed by firearm manufacturer Heckler & Koch, Dynamit Nobel, and Hensoldt Wetzlar. The rifle is noted for its use of caseless ammunition.
The Fucile Mitragliatore Breda modello 30 also known as Breda 30 or the Alpine scythe (la falce degli Alpini) or Finita Burrasca (The storm is over) was the standard light machine gun of the Royal Italian Army during World War II. The Breda Modello 30 was issued at platoon level and gave Italian rifle squads extra firepower. As a light machine gun it had many problems including jamming and overheating. It was fed by a 20 round stripper clips which had to be oiled by a lubrication device. Despite all its faults it formed the main base of fire for infantry units during the war.
A magazine, often simply called a mag, is an ammunition storage and feeding device for a repeating firearm, either integral within the gun or externally attached. The magazine functions by holding several cartridges within itself and sequentially pushing each one into a position where it may be readily loaded into the barrel chamber by the firearm's moving action. The detachable magazine is sometimes colloquially referred to as a "clip", although this is technically inaccurate since a clip is actually an accessory device used to help load ammunition into a magazine or cylinder.
The ArmaLite AR-10 is a 7.62×51mm NATO battle rifle designed by Eugene Stoner in the late 1950s and manufactured by ArmaLite. When first introduced in 1956, the AR-10 used an innovative combination of a straight-line barrel/stock design with phenolic composite, a new patent-filed gas-operated bolt and carrier system and forged alloy parts resulting in a small arm significantly easier to control in automatic fire and over 1 lb (0.45 kg) lighter than other infantry rifles of the day. Over its production life, the original AR-10 was built in relatively small numbers, with fewer than 10,000 rifles assembled. However, the ArmaLite AR-10 would become the progenitor for a wide range of firearms.
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 cartridge from the magazine or belt into the chamber, and fires that cartridge in the same movement. Like any other self-loading design, the action is cycled by the energy released from the propellant, which sends the bolt back to the rear, compressing the mainspring in readiness for firing the next round. In an open-bolt gun firing semi-automatically, the bolt is caught and held at this point by the sear after each shot; and in automatic open-bolt fire, it's caught and held in this manner whenever the trigger is released. In contrast to this, in closed-bolt guns, the trigger and sear do not affect the movement of the bolt directly.
The Beta C-Mag is a 100-round capacity drum magazine manufactured by the Beta Company. It was designed by Jim Sullivan and first patented in 1987 and has been adapted for use in numerous firearms firing the 5.56×45mm NATO, 7.62×51mm NATO, and 9×19mm Parabellum cartridges. C-Mag is short for century magazine, referring to its 100-round capacity. It has two drum units, each of which hold half of the cartridges inserted into the magazine. The latest version of the magazine is available with a transparent backing to allow the user to see the number of rounds remaining in the magazine. A C-Mag loaded with 5.56×45mm NATO ammunition typically weighs about 2.1 kg (4.63 lb); a C-Mag loaded with 7.62×51mm NATO ammunition weighs 4.77 kg (10.5 lb).
The Stoner 63 is a 5.56×45mm NATO modular weapon system. Using a variety of modular components, it can be configured as an assault rifle, carbine, top-fed light machine gun, belt-fed squad automatic weapon, or as a vehicle mounted weapon. Also known as the M63, XM22, XM23, XM207 or the Mk 23 Mod 0 machine gun, it was designed by Eugene Stoner in the early 1960s. Cadillac Gage was the primary manufacturer of the Stoner 63 during its history. The Stoner 63 saw very limited combat use by US military units during the Vietnam War. A few were also sold to law enforcement agencies.
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.
A breechblock is the part of the firearm action that closes the breech of a breech loading weapon before or at the moment of firing. It seals the breech and contains the pressure generated by the ignited propellant. Retracting the breechblock allows the chamber to be loaded with a cartridge.
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 case and insert a new cartridge into the chamber. Energy from the gas is harnessed through either a port in the barrel or a trap at the muzzle. This high-pressure gas impinges on a surface such as a piston head to provide motion for unlocking of the action, extraction of the spent case, ejection, cocking of the hammer or striker, chambering of a fresh cartridge, and locking of the action.
The Heckler & Koch MG4 is a belt-fed 5.56 mm light machine gun designed and developed by German firearm manufacturer Heckler & Koch. It was developed in the late 1990s and first seen publicly in September 2001. It has been selected to replace the 7.62 mm MG3 general-purpose machine gun in the Bundeswehr at the squad support level; it will complement the MG3 in other roles. It will also be the secondary armament of the new Puma infantry fighting vehicle. Overall, it is designed to be light, provide maximum safety to the user and function reliably under adverse conditions using a wide range of ammunition from different manufacturers, without the need to adjust the gas system. It was known as the MG43 prior to its adoption by the Bundeswehr.
The M1941 Johnson Light Machine Gun, also known as the Johnson and the Johnny gun, was an American recoil-operated light machine gun designed by Melvin Johnson in the late 1930s. It shared the same operating principle and many parts with Malvin's M1941 Johnson rifle and M1947 Johnson auto carbine.
Rotating bolt is a method of locking the breech 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 rather than lugs on the bolt head like the Mauser M 98 or M16. The first rotating bolt rifle with two lugs on the bolt head was the Lebel Model 1886 rifle. The concept has been implemented on most firearms chambered for high-powered cartridges since the 20th century.
The Colt Automatic Rifle or Colt Light Machine Gun is a 5.56 mm NATO, open-bolt, full-automatic-only firearm developed by Colt Defense. It is based on the M16A2/A4, and has a distinctive squared-off handguard, vertical grip, carrying handle and integrated bipod.
The Heckler & Koch MG5 is a belt-fed 7.62×51mm NATO general-purpose machine gun manufactured by German firearm manufacturer Heckler & Koch. The MG5 resembles the 5.56×45mm NATO Heckler & Koch MG4 light machine gun, which was adopted into German military service in 2015.