Self-loading rifle

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A self-loading rifle is a rifle in which the next cartridge is loaded into the chamber from the magazine as part of the action of the weapon upon firing a shot. Self-loading actions include both automatic and semi-automatic. In a semi-automatic weapon, once loaded and cocked, each depression of the trigger will fire one shot, while an automatic firearm will continue to discharge rounds as the mechanism cycles, until the magazine is emptied or the trigger is released. They may be operated by a number of mechanisms, all of which derive their power from the explosion of the powder in the cartridge that also fires the bullet. Historically, the self-loading design was the successor to the repeating rifle, which stored a number of cartridges within the weapon, but required manual action to load a fresh cartridge before each shot. Automatically loading the next round more easily allows for rapid fire.

Mechanisms

Gas operated

Main articles: Blowback, Gas actuated

In a gas-operated mechanism, a portion of the gases propelling the bullet from the barrel are extracted and sent back to the rear of the rifle, where they operate a piston. The motion of this piston in turn unlocks and operates the bolt, which performs extraction of the spent cartridge and via spring action readies the next round. Almost all modern military rifles use mechanisms of this type.

Recoil operated

In some small caliber weapons, the bolt is not restrained but is relatively heavy and held against the breech by a spring. The gas pressure in the cartridge and the weapon recoil acts to push the bolt back, but owing to inertia this action does not significantly cause loss of gas pressure until after the bullet has left the barrel. Subsequent action is similar to that of the gas operated mechanism. This type of action is simple and inexpensive to manufacture, but is limited in the power it can handle, so it is seen on small caliber weapons such as machine pistols and submachine guns.

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