Semi-automatic firearm
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A semi-automatic firearm is one that requires only a trigger pull for each round that is fired, unlike a single-action revolver, a pump-action firearm, a bolt-action firearm, or a lever-action firearm, which require the shooter to manually chamber each successive round. For instance, if someone were to shoot ten rounds in a semi-automatic firearm, they would need to pull the trigger ten times (once for each round fired), as opposed to a fully-automatic firearm, which will continue to fire as long as the trigger is held or until it runs out of ammunition.
Firearms firing bursts of more than one round (usually three) per pull of the trigger, such as the M16A2 rifle, are generally considered fully-automatic. Pistols, rifles, and shotguns can all be semi-automatic. A semi-automatic option is a common choice on selective fire firearms.
Semi-automatic weapons are sometimes divided into two categories: those that fire from an open bolt and those that fire from a closed bolt. When the trigger is pulled, the open bolt flies forward, picking up a cartridge from the magazine and ramming it into the chamber and the gun fires. The closed bolt system moves the bolt forward and picks up the cartridge as the last phases of the previous cycle, and when the trigger is pulled again only the firing pin moves. The closed bolt system is generally more accurate, since the center of gravity changes relatively little. The open bolt system is almost exclusively used in submachine guns and support weapons, as it also lets the barrel cool more quickly.
There is some casual dispute over the correct use of the words automatic and semi-automatic. Gun enthusiasts sometimes argue that the word automatic is incorrectly linked to fully-automatic fire and that an automatic weapon is simply any weapon that chambers a new round during the extraction of the previous cartridge's casing. The term is often used to mean a self-loading semi-automatic firearm rather than a fully-automatic one. One narrow definition would be that a semi-automatic firearm would thus be a weapon using the open bolt system, and the semi-automatic function is simply the removal of the case, whereas an automatic weapon would both remove the empty case and chamber a fresh cartridge. In practice, an automatic pistol usually means a self-loading semi-automatic pistol but an automatic rifle usually means one capable of fully-automatic fire. Both uses can be found, and the exact meaning must be determined from context. Among U.S. law enforcement practitioners, in which the use of double-action revolvers has almost entirely disappeared, the term "automatic pistol" has been surplanted by the jargon term "auto-loader".
Some semi-automatic firearms with features commonly found on military or law-enforcement firearms are often referred to as assault weapons in America.
See also
nl:Semi-automatisch wapen sl:Polavtomatsko orožje no:Halvautomatisk skytevåpen