Semi-automatic firearm

A semi-automatic, or self-loading firearm is a gun 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 example, to fire ten rounds in a semi-automatic firearm, the trigger would need to be pulled ten times (once for each round fired), in contrast to a fully automatic firearm, which can continue to fire as long as the trigger is held or until it runs out of ammunition.

Semi-automatic weapons
There are semi-automatic pistols, rifles, and shotguns. A semi-automatic mode is a common choice on selective fire firearms. Firearms capable of firing bursts of more than one round (usually three) per pull of the trigger, such as the M16A2 rifle, are considered fully automatic.

Semi-automatic triggers
A double-action revolver also requires only a trigger pull for each round that is fired but is not considered semi-automatic. The difference in a double-action revolver is that the act of pulling the trigger also rotates the cylinder moving the next round into position. Semi-automatic function uses the recoil force generated by the last fired cartridge combined with spring action in the firearm to ready the next round to be fired.

Fully Automatic compared to Semi-automatic
The usage of the term automatic may vary according to context. Gun specialists point out that the word automatic is sometimes misunderstood to mean fully automatic fire when used to refer to a self-loading, semi-automatic firearm not capable of fully automatic fire. In this case, automatic refers to the loading mechanism, not the firing capability.

The term "automatic pistol" almost exclusively refers to a semi-automatic (i.e. not fully automatic) pistol. With handguns, the term "automatic" is commonly used to distinguish semi-automatic pistols from revolvers. The term "auto-loader" may also be used to describe a semi-automatic handgun. However, the term "automatic rifle" may mean a rifle capable of fully automatic fire. Both uses of the term "automatic" can be found, and the exact meaning must be determined from context.

Semi-automatic
The mechanism of semi-automatic (or auto-loading) firearms is usually what is known as a closed bolt firing system. In a closed-bolt system, a round must first be chambered manually before the weapon can fire. When the trigger is pulled, only the hammer and firing pin move, striking and firing the cartridge. The bolt then recoils far enough rearward to extract and load a new cartridge from the magazine into the firearm's chamber, ready to fire again once the trigger is pulled.

An open bolt mechanism is a common characteristic of fully automatic firearms. With this system, pulling the trigger releases the bolt from a cocked, rearward position, pushing a cartridge from the magazine into the chamber, firing the gun. The bolt retracts to the rearward position, ready to strip the next cartridge from the magazine. The open-bolt system is often used in submachine guns and other weapons with a high rate of fire. It is rarely used in semi-automatic-only firearms, which can fire only one shot with each pull of the trigger. The closed-bolt system is generally more accurate, since the center of gravity changes relatively little at the moment the trigger is pulled.

Semi-automatic rifle
The first successful design for a semi-automatic rifle is attributed to German-born gunsmith Ferdinand Ritter von Mannlicher, who unveiled the design in 1885. Although Mannlicher earned his reputation with his bolt action rifle designs, he also produced a few semi-automatic pistols, including the Steyr Mannlicher M1894, which employed an unusual blow-forward action and held five rounds of 6.5mm ammunition that were fed into the M1894 by a stripper clip.

Semi-automatic shotgun
A few years later, American gunsmith John Moses Browning developed the first successful semi-automatic shotgun, the Browning Auto-5, which was first manufactured in 1902 by Fabrique Nationale de Herstal and sold in America under the Browning name. The Auto-5 relied on long recoil operation; this design remained the dominant form in semi-automatic shotguns for approximately 50 years. Production of the Auto-5 was finally ceased in 1999.

Blow-back semi-automatic
In 1903 and 1905, the Winchester Repeating Arms Company introduced the first semi-automatic rim-fire and center-fire rifles designed especially for the civilian market. The Winchester Model 1903 and Model 1905 operated on the principle of delayed blow-back in order to function semi-automatically. Designed entirely by T.C. Johnson, the Model 1903 achieved commercial success and continued to be manufactured to 1932 when it was replaced by the Winchester Model 63.

Rifles
In 1906, Remington Arms introduced the "Remington Auto-loading Repeating Rifle," also designed by Browning. This rifle, renamed the "Model 8" in 1911, was advertised as a sporting rifle by Remington. The rifle was offered in .25, .30, .32, and .35 caliber models, and gained popularity among civilians as well as some law enforcement officials who appreciated the combination of semi-automatic action and relatively powerful rifle cartridges. The Model 8 was superseded in 1936 by the Model 81.

The first semi-automatic rifle adopted and used by a major military Power (France) was Fusil Automatique Modele 1917. It was the first general issue self loading rifle and contained features that were seminal in its field. Features first found on the M1917 would later find their way into many later, more widely known, more widely produced designs. Like a venerable patriarch, the M1917 deserves recognition and respect as one of the most important and influential military longarms ever devised. Though the Garand is usually considered by some to be the first issued as a standard infantry weapon, the M1917 predates it and was used in the latter stages of WW1 and the Moroccan Rif war 1921-1926. The Garand was the gas-operated M1 Garand, developed by Canadian-born John Garand for Springfield Armory, which was owned by the US government. After years of research and testing, the first production model of the M1 Garand was unveiled in 1937. During World War II, the M1 Garand gave American infantrymen an overall advantage over their German opponents, many of whom still used the Mauser 98 bolt action rifle.