Semi-automatic firearm

A semi-automatic firearm, also called self-loading firearm or autoloading firearm (though fully automatic and selective fire firearms are technically also self-loading), is one whose action mechanism automatically loads a following round of cartridge into the chamber (self-loading) and prepares it for subsequent firing, but requires the shooter to manually actuate the trigger in order to discharge each shot. Typically, this involves the weapon's action utilizing the excess energy released during the preceding shot (in the form of recoil or high-pressure gas expanding within the bore) to unlock and move the bolt, extracting and ejecting the spent cartridge case from the chamber, re-cocking the firing mechanism, and loading a new cartridge into the firing chamber, all without input from the user. To fire again, however, the user must exert effort to actively release the trigger, allow it to "reset", before pulling the trigger again to fire off the next round. As a result, each trigger-pull only discharges a single round from a semi-automatic weapon, as opposed to a fully automatic weapon, which will shoot continuously as long as the ammunitions are replete and the trigger is kept depressed.

Ferdinand Ritter von Mannlicher produced the first successful design for a semi-automatic rifle in 1885, and by the early 20th century, many manufacturers had introduced semi-automatic shotguns, rifles and pistols.

In military use, self-loading rifles were in the minority in World War II with most armies chiefly reliant upon manually loaded bolt-action rifles.

Early history (1885–1945)
The Fusil Automatique Modele 1917 was the first semi-automatic gun that fires cartridges to be widely issued in the infantry of any nation's army.

The first successful design for a semi-automatic rifle is attributed to Austria-born gunsmith Ferdinand Ritter von Mannlicher, who unveiled the design in 1885.[1] The Model 85 was followed by the equally innovative Mannlicher Models 91, 93 and 95 semi-automatic rifles.[2] 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 6.5 mm ammunition that were fed into the M1894 by a stripper clip.

Semi-automatic shotgun
Remington 1100 Tactical Shotgun in 12 gauge – an example of a 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 ended in 1999.

Blowback semi-automatic

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

By the early 20th century, several manufacturers had introduced semi-automatic .22 sporting rifles, including Winchester, Remington, Fabrique Nationale and Savage Arms, all using the direct blow-back system of operation. Winchester introduced a medium caliber semi-automatic sporting rifle, the Model 1907 as an upgrade to the Model 1905, utilizing a blowback system of operation, in calibers such as .351 Winchester. Both the Models of 1905 and 1907 saw limited military and police use.

Notable early semi-automatic rifles

In 1906, Remington Arms introduced the "Remington Auto-loading Repeating Rifle." Remington advertised this rifle, renamed the "Model 8" in 1911, as a sporting rifle. This is a locked-breech, long recoil action designed by John Browning. 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 a semi-automatic action and relatively powerful rifle cartridges. The Model 81 superseded the Model 8 in 1936 and was offered in .300 Savage as well as the original Remington calibers.

The first semi-automatic rifle adopted and widely issued by a major military power (France) was the Fusil Automatique Modele 1917. This is a locked-breech, gas-operated action which is very similar in its mechanical principles to the future M1 Garand in the United States. The M1917 was fielded during the latter stages of World War I but it did not receive a favorable reception. However its shortened and improved version, the Model 1918, was much more favourably received during the Moroccan Rif War from 1920 to 1926. The Lebel bolt-action rifle remained the standard French infantry rifle until replaced in 1936 by the MAS-36 despite the various semi-automatic rifles designed between 1918 and 1935.

Other nations experimented with self-loading rifles between the two World Wars, including the United Kingdom, which had intended to replace the bolt-action Lee–Enfield with a self-loader, possibly chambered for sub-caliber ammunition, but discarded that plan as the imminence of the Second World War and the emphasis shifted from replacing every rifle with a new design to speeding-up re-armament with existing weapons. The Soviet Union and Nazi Germany would both issue successful self-loading and selective-fire rifles on a large scale during the course of the war, but not in sufficient numbers to replace their standard bolt-action rifles.

Notable gas-operated rifles
The SKS is a semi-automatic Russian rifle

In 1937, the American M1 Garand was the first semi-automatic rifle to replace its nation's bolt-action rifle as the standard-issue infantry weapon. The gas-operated M1 Garand was developed by Canadian-born John Garand for the U.S. government at the Springfield Armory in Springfield, Massachusetts. 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 advantage over their opponents, most of whom were issued slower firing bolt-action rifles.[3]

The Soviet AVS-36, SVT-38 and SVT-40 (originally intended to replace the Mosin-Nagant as their standard service rifle), as well as the German Gewehr 43, were semi-automatic gas-operated rifles issued during World War II. In practice, they did not replace the bolt-action rifle as a standard infantry weapon.

Another gas-operated semi-automatic rifle developed toward the end of World War II was the SKS. Designed by Sergei Gavrilovich Simonov in 1945, it came equipped with a bayonet and could be loaded with ten rounds, using a stripper clip. However, the SKS was quickly replaced by the AK-47. It was the first widely issued weapon to use the 7.62×39mm cartridge.

Types
SIG Pro semi-automatic pistol

There are semi-automatic pistols, rifles, and shotguns designed and made as semi-automatic only. Selective-fire firearms are capable of both full automatic and semi-automatic modes.

Semi-automatic refers to a firearm which uses the force of recoil or gas to eject the empty case and load a fresh cartridge into the firing chamber for the next shot and which allows repeat shots solely through the action of pulling the trigger. A double-action revolver also requires only a trigger pull for each round that is fired but is not considered semi-automatic since the manual action of pulling the trigger is what advances the cylinder, not the energy of the preceding shot.

Fully automatic compared to semi-automatic
Walther P99, a semi-automatic pistol from the late 1990s
Glock 18, a fully-automatic machine pistol from the mid 1980s (The picture shown is the Glock 18C)

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. To avoid confusion, it is common to refer to such firearms as an "autoloader" in reference to its loading mechanism.

The term "automatic pistol" almost exclusively refers to a semi-automatic (i.e. not fully automatic) pistol (fully automatic pistols are usually referred to as machine pistols). 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, to avoid confusion, the term "automatic rifle" is generally, conventionally and best restricted to a rifle capable of fully automatic fire. Both uses of the term "automatic" can be found; the exact meaning must be determined from context.

Auto-loading

The mechanism of semi-automatic (or autoloading) 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, as the centre of gravity changes relatively little at the moment the trigger is pulled.

With fully automatic weapons, open-bolt operation allows air to circulate, cooling the barrel; with semi-automatic firearms, the closed-bolt operation is preferred, as overheating is not as critical, and accuracy is preferred. Some select-fire military weapons use an open bolt in fully automatic mode and a closed bolt when semi-automatic is selected.

Examples
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See also

References
  1. Jewison, Glenn; Steiner, Jörg C. (2010). "Ferdinand Ritter von Mannlicher". austro-hungarian-army.co.uk. Glenn Jewison.
  2. Smith, Walter H.B. (1947). Mannlicher Rifles and Pistols: Famous Sporting and Military Weapons. Military Service Publishing.
  3. "Firsts: Springfield 375". 2011. Archived from the original on March 14, 2012.
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