An automatic firearm continuously fires rounds as long as the trigger is pressed or held and there is ammunition in the magazine/chamber. In contrast, a semi-automatic firearm fires one round with each individual trigger-pull.
Although all "semi-automatic", "burst fire", and "fully automatic" firearms are "automatic" in the technical sense that the firearm automatically cycles between rounds with each trigger pull, the terms "automatic weapon" and "automatic firearm" are conventionally reserved by firearm enthusiasts to describe fully automatic firearms. Use of the terms "fully automatic" or "full auto" can avoid confusion. Firearms are further defined by the type of firearm action used.
Self-loading firearms are designed with varying rates of fire due to having different purposes. The speed with which a self-loading firearm can cycle through the functions of:
is called the cyclic rate. In fully automatic firearms the cyclic rate is tailored to the purpose that the gun is made to serve. Anti-aircraft machine guns often have extremely high rates of fire to maximize the probability of a hit. In infantry support weapons these rates of fire are often much lower and in some cases variable within the design of the firearm. The MG 34 is a WWII-era machine gun which today would be referred to as a general purpose machine gun. It came in several variations with a cyclic rate as high as 1200 rounds per minute, but also made an infantry model which fired at 900 rounds per minute. 
Firing any firearm generates a very high temperature in the firearm's barrel and elevated temperature throughout much of its structure. If fired too fast, the components of the firearm will suffer a structural failure. This means that all firearms, regardless of whether they are semi-automatic, fully automatic, or burst mode in their firing methods, will overheat and fail if fired too often. This is especially a problem with fully automatic fire. In actual use (for example the MG34), a gun might be able to fire at 1200 rounds per minute, but in one minute it may also overheat and fail. So guns used in a repeated firing mode must not be fired too often. The MG34 is fired manually in bursts of 5 to 7 rounds (no automatic disconnector mode in this gun). It can fire at an effective rate of 150 rounds per minute.
Similarly semi-automatic firearms will also overheat if not allowed to cool. A semi-automatic rifle typically has an effective firing rate of 40 rounds per minute. A large part of the reason that this is so low, is that the recoil of firing a round pushes the gun's aim off target. The time it takes to "reacquire" the target slows the effective firing rate. The Army Study Guide lists the sustained rate of fire for an M4 Rifle at 12 to 15 rounds per minute.
Automatic firearms can be divided into six main categories:
Burst mode is often used in military firearms to limit the number of rounds fired due to the inaccuracy of fully automatic fire. In the US M16/M4 rifles for example, the burst mode is 3 rounds. The trigger once pulled and held, results in 3 rounds being fired. The gun will not fire again until the trigger is released and then pulled again. There are suggestions that fully automatic fire has no genuine benefit and has been restricted or banned in combat due to being a waste of ammunition. The US M4 Carbine is now the main combat rifle of the US armed forces and has been available until recently in semi-automatic and burst mode of 3 rounds only.
Automatic weapons tend to be restricted to military and police organizations in most developed countries that permit the use of semi-automatic firearms. Where automatic weapons are permitted, restrictions and regulations on their possession and use may be much more severe than for other firearms. In the United States, taxes and strict regulations affect the manufacture and sale of fully automatic firearms under the National Firearms Act. A prospective user must go through an application process administered by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), which requires a federal tax payment of $200 and a thorough criminal background check. The tax payment buys a revenue stamp, which is the legal document allowing possession of an automatic firearm. The use of a gun trust to register with the BATFE has become an increasingly popular method of acquisition and ownership of automatic firearms.
Other similar weapons not usually called automatic firearms are the following:
The ArmaLite AR-7 Explorer is a semi-automatic firearm in .22 Long Rifle caliber, developed in 1959 from the AR-5 that was adopted by the U.S. Air Force as a pilot and aircrew survival weapon. The AR-7 was adopted and modified by the Israeli Air Force as an aircrew survival weapon in the 1980s.
The AR-7 was designed by American firearms designer Eugene Stoner, who is most associated with the development of the ArmaLite AR-15 rifle that was adopted by the US military as the M16. The civilian AR-7's intended markets today are backpackers and other recreational users as a takedown utility rifle. The AR-7 is often recommended for use by outdoor users of recreational vehicles (automobile, airplane or boat) who might have need for a weapon for foraging or defense in a wilderness emergency.Automatic rifle
An automatic rifle is a type of self-loading rifle that is capable of automatic fire. Automatic rifles are select-fire weapons that are capable of firing in semi-automatic and automatic firing modes (some automatic rifles are capable of burst-fire as well). Automatic rifles are distinguished from semi-automatic rifles in their ability to fire more than one shot in succession once the trigger is pulled. Most automatic rifles are further subcategorized as battle rifles or assault rifles.Automatic shotgun
An automatic shotgun is an automatic firearm that fires shotgun shells and uses some of the energy of each shot to automatically cycle the action and load a new round. It will fire repeatedly until the trigger is released or ammunition runs out. Automatic shotguns have a very limited range, but provide tremendous firepower at close range.Bump fire
Bump fire is the act of using the recoil of a semi-automatic firearm or revolver to fire shots in rapid succession at the cost of accuracy of individual shots.
Bump fire gunstocks are of varying legality in the United States. Following the 2017 Las Vegas shooting, the Department of Justice announced a plan on March 23, 2018, to classify bump stocks as "machine guns" and effectively ban them nationwide under existing federal law. If the rule becomes final, existing bump stocks would require a license, or one to have a Federal Firearm License to legally own and would otherwise be required to be destroyed or surrendered by both manufacturers and individual owners. The Department of Justice announced on December 18, 2018, that bump stocks would be regulated like machine guns by March 26, 2019.On April 17, 2018, Slide Fire Solutions, the sole holder of the bump stock patent, announced that it would cease production of bump stocks as of May 20, though they did not state whether this was a temporary or permanent measure. It has temporarily suspended production before.Closed bolt
A semi or full-automatic firearm which is said to fire from a closed bolt is one where, when ready to fire, a round is in the chamber and the bolt and working parts are forward. 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, the bolt then 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. The Maxim style arms used by both the Allies, as the Vickers machine gun and Central Powers, as both the rectangular-receiver lMG 08 and lightened-receiver LMG 08/15 Spandau gun, and Parabellum LMG 14 gun — as well as the improvements introduced by Swedish armaments designer Carl Gustave Swebilius to the American M1895 Colt–Browning machine gun for aircraft use, creating the M1917 and M1918 Marlin machine guns for the USAAS in World War I — all 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.Hell-Fire trigger
A Hell-Fire trigger is a device that allows a semi-automatic firearm to fire at a rate approaching that of a fully automatic firearm. The Hell-Fire trigger system is ATF legal. The Hell-Fire installs in seconds and clamps to the trigger guard behind the trigger. It has a "finger" that presses against the back of the trigger. The net effect of this is to increase the force that attempts to return the trigger to its forward position. For operation, the gun is held loosely with the non-trigger hand and the trigger finger held stiffly. When firing commences, the weapon will recoil and the device is pressed against the trigger. The tension arm in the device causes the gun to move forward again, causing the trigger to be pressed against the trigger finger again. The system utilizes the gun's own recoil and inertia. This rapid firing prevents aiming with the sights, making accurate shooting impossible.Technically, the firearm is not altered. As in all semi-automatic firearms, only one round is fired with every stroke of the trigger.
The Hell-Fire trigger was used, with a pair of TEC-9 pistols, by the perpetrator of a 1993 mass shooting that killed nine people. Separately, David Koresh, leader of the Branch Davidians, reportedly told authorities that he utilized semi-automatic guns with the part installed.Hellfire
Hellfire may refer to:
The fires of Hell or lake of fire, terms used to describe Hell. Also sometimes referred to as "The Flame of The Dead" Due to its links to the underworld.John T. Kewish
John T. Kewish was an American inventor and the principal creator of the primer actuated machine gun in 1918, covered by U.S. patent no. 1,472,126. John C. Garand was assigned 25% as co-inventor. Kewish was also a contributor to several later automatic firearm developments.Kel-Tec SUB-2000
The SUB-2000 is a pistol-caliber carbine manufactured by Kel-Tec CNC Industries of Cocoa, Florida, United States. The rifle is a blowback operated, semi-automatic firearm with its operating spring located in the tubular stock.
The weapon feeds from a grip-located magazine well, using magazines designed for popular models of various other manufacturer's handguns, and is an inexpensive carbine. The distinguishing characteristic of this rifle is that it folds in half, for storage and transportation, and its slim profile compared to other rifles. The benefit of the weapon accepting magazines made for other manufacturer's popular handguns is so the user can choose a version of the weapon that allows them to share magazines and ammunition between both the user's sidearm and the Sub-2000 carbine. The main advantages of a carbine in a pistol caliber over a handgun include the increased sight radius which aids with accurate shooting; the long barrel more efficiently captures burning powder which increases projectile velocity; and more points of contact between the shooter and weapon which increases stability.Medium machine gun
A medium machine gun (MMG), in modern terms, usually refers to a belt-fed automatic firearm firing a full-power rifle cartridge.Military-style semi-automatic
Military style semi-automatic firearm is a phrase used in New Zealand to describe semi-automatic firearms usually known as assault weapons in the United States. The phrase is often abbreviated as military style semi-automatic or MSSA. A New Zealand firearms licence holder requires an E Category endorsement on their licence before they can possess this type of firearm and a Police issued permit to procure each firearm is required. Some semi-automatic firearms that have been sold in a sporting configuration, so that they can be possessed by a person holding a standard firearms licence, without endorsements, can be converted to an MSSA simply by adding or changing one part, such as a larger magazine or flash suppressor. If a person intends to convert an A Category firearm they already possess they need to obtain an E Category endorsement before making the conversion to their firearm, because merely having parts in the person's possession to make the conversion possible makes an A Category semi-automatic firearm an MSSA.The phrase was introduced as part of the 1992 amendment to the Arms Act that was intended to impose stricter controls on military style semi-automatic firearms following the 1990 Aramoana massacre where a lone gunman, who held a lifetime firearms licence, killed 13 people using several different firearms, including a semi-automatic rifle that he fired from the hip at police. Arriving at a clear definition and common understanding of which semi-automatic firearms have a military style configuration has dominated debate about gun control legislation in New Zealand since 1992.Open bolt
A fully automatic firearm is said to fire from an open bolt 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 gas expended from the round, hence the necessity of a gas system; this excess of gas sends the bolt back to the rear, ejecting the empty cartridge case and preparing for the next shot (or continuing forward again, if the trigger is held down in turn keeping the catch depressed and the weapon is an automatic). Generally, an open-bolt firing cycle is used for fully automatic weapons and not for semi-automatic weapons (except some semi-automatic conversions of automatic designs). Firearms using advanced primer ignition blowback inherently fire from open bolt only.Semi
Semi may refer to:
semi-, numerical prefix meaning "half"
Semiconductor industry, also known as semi or semis in financial news
Semi-detached house, a type of housing
Semi-final, of a knockout competition
Semi-formal, (esp. high school) dance
Semi-submersible, a watercraft
Semi-trailer truck (UK: articulated lorry)
Semiquaver, the time interval in music, which is half the length of a quaver
Semi-erection, a partial erection when the penis is enlarged but not fully erect
Tesla Semi, vehicle by Tesla, Inc.
Semi Ojeleye (born 1994), American basketball player
Semiconductor Equipment and Materials International (SEMI)Semi-automatic
Semi-automatic may refer to:
A semi-automatic firearm, a firearm which automatically reloads, but will only fire one round per trigger pull
Semiautomatic switching system, a term used in telecommunication
Semi-automatic transmission, a vehicle transmission with no clutch pedalSemi-automatic firearm
A semi-automatic firearm, also called self-loading firearm or autoloading firearm (though fully automatic and selective fire firearms technically are also self-loading), is one that not only fires a bullet each time the trigger is pulled, but also performs all steps necessary to prepare it to discharge again—assuming cartridges remain in the firearm's feed device. Typically, this includes extracting and ejecting the spent cartridge case from the firing chamber, re-cocking the firing mechanism, and loading a new cartridge into the firing chamber. To fire again, the trigger is released and re-pressed.
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 barely used in World War I, and most armies in World War II also still relied upon bolt-action rifles, with the exception of the Americans, who in 1937 had adopted the M1 Garand as the standard-issue infantry weapon.Spray and pray
Spray and pray is a derisive term for firing an automatic firearm towards an enemy in long bursts, without making an effort to line up each shot or burst of shots. This is especially prevalent amongst those without benefit of proper training. It differs from suppressive fire as the shooting is sloppily directed. This term does not apply to appropriately focused fully automatic fire or true suppressive fire, which is standard practice for a properly trained combatant.
In the Rhodesian Bush War and elsewhere, spray and pray was used to describe the firing of a relatively inaccurate weapon.
Jack Lewis a former U.S. Marine veteran of World War II, the Korean War, and Vietnam War and editor of Gun World magazine met the then Commandant of the Marine Corps Paul X. Kelley. Lewis told the Commandant that the effect of the introduction of the M16 rifle was that "The United States used to be known as a Nation of Riflemen; now we've become a Nation of Sprayers".Drawbacks of uncontrolled automatic gunfire are the low likelihood of actually hitting an enemy target, the large amounts of ammunition needed, and the increased risk of it becoming friendly fire. It was due to the tendency of soldiers to spray and pray during the Vietnam War that the US replaced the automatic-fire setting that was on the original M16 with three-round burst fire for the M16A2 and M16A4/M4 carbine.Squad automatic weapon
A squad automatic weapon, also section automatic weapon [SAW]; light support weapon [LSW]) is a fully automatic firearm used to give infantry squads or sections a man-portable source of fully automatic firepower. Weapons used in this role are often selective-fire rifles, usually fitted with a bipod and heavier barrel to perform as light machine guns. Squad automatic weapons usually fire the same cartridge as the assault rifles or battle rifles carried by other members of the unit. This reduces logistical requirements by making it only necessary to supply one type of ammunition to a unit. Squad automatic weapons are light enough to be operated by one person, as opposed to heavy machine guns such as the M2 Browning, which fire more powerful cartridges but require a crew to operate at full effectiveness.Villar Perosa aircraft submachine gun
The Villar Perosa M15 was an Italian portable automatic firearm developed during World War I by the Officine di Villar Perosa.
Originally designed to be used by the second crew member/observer of military airplanes, it was later issued to ground troops. Between May and November 1916 a section was assigned to each infantry battalion of the Italian army and from May 1917 the number of sections was increased to 3 per battalion.
While it was designed to use 9mm pistol ammunition, it is said to be the first true submachine gun.Winchester Model 1903
The Winchester Model 1903 was the first commercially available semi-automatic firearm made by the Winchester Repeating Arms Company.