An automatic firearm is an auto-loading

firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...

that continuously chambers and fires rounds when the trigger mechanism is actuated. The action of an automatic firearm is capable of harvesting the excess energy released from a previous discharge to feed a new

ammunition Ammunition (informally ammo) is the material fired, scattered, dropped, or detonated from any weapon or weapon system. Ammunition is both expendable weapons (e.g., bombs, missiles, grenades, land mines) and the component parts of other we ...

round into the

chamber Chamber or the chamber may refer to: In government and organizations *Chamber of commerce, an organization of business owners to promote commercial interests *Legislative chamber, in politics *Debate chamber, the space or room that houses deliber ...

, and then ignite the

propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the ...

and discharge the

projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found i ...

(either

bullet A bullet is a kinetic projectile, a component of firearm ammunition that is shot from a gun barrel. Bullets are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax. Bullets are made in various shapes and co ...

, shot, or

slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a ...

) by delivering a hammer or striker impact on the

primer Primer may refer to: Arts, entertainment, and media Films * ''Primer'' (film), a 2004 feature film written and directed by Shane Carruth * ''Primer'' (video), a documentary about the funk band Living Colour Literature * Primer (textbook), a te ...

. If ''both'' the feeding and ignition procedures are automatically cycled, the weapon will be considered "fully automatic" and will fire continuously as long as the trigger is kept depressed and the ammunition feeding (either from a

magazine A magazine is a periodical publication, generally published on a regular schedule (often weekly or monthly), containing a variety of content. They are generally financed by advertising, purchase price, prepaid subscriptions, or by a combinatio ...

or a

belt Belt may refer to: Apparel * Belt (clothing), a leather or fabric band worn around the waist * Championship belt, a type of trophy used primarily in combat sports * Colored belts, such as a black belt or red belt, worn by martial arts practiti ...

) remains available. In contrast, a firearm is considered " semi-automatic" if it only automatically cycles to chamber new rounds (i.e.

self-loading A semi-automatic firearm, also called a self-loading or autoloading firearm (fully automatic and selective fire firearms are also variations on self-loading firearms), is a repeating firearm whose action mechanism ''automatically'' loads a follow ...

) but does not automatically fire off the shot unless the user manually resets (usually by releasing) and re-actuates the trigger, so only one round gets discharged with each individual trigger-pull. A burst-fire firearm is an "in-between" of fully and semi-automatic firearms, firing a brief continuous "burst" of multiple rounds with each trigger-pull, but then will require a manual re-actuation of the trigger to fire another burst. Automatic firearms are further defined by the type of cycling principles used, such as recoil operation, blowback,

blow-forward Blow-forward is a firearm action where the propellant gas pressure and the friction of the bullet traveling down the bore drag the whole gun barrel forward to facilitate the opening of the breech. This forward barrel motion provides most o ...

gas operation Gas-operation is a system of operation used to provide energy to operate locked breech, autoloading firearms. In gas-operation, a portion of high-pressure gas from the cartridge being fired is used to power a mechanism to dispose of the spent ...

Rates of fire

Cyclic rate

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: #Fire #Eject #Load #Cock is referred to as its cyclic rate. In fully automatic firearms, the cyclic rate is tailored to the purpose the firearm is intended 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, vary with the design of the particular firearm. The MG 34 is a

WWII World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

-era machine gun which falls under the category of a "general purpose machine gun". It was manufactured in several variations: with a cyclic rate as high as 1200 rounds per minute, but also in an infantry model which fired at 900 rounds per minute.

Effective rate of fire

Continuous fire generates high temperatures in a firearm's barrel and increased temperatures throughout most of its structure. If fired continuously, the components of the firearm will eventually suffer structural failure. All firearms, whether they are semi-automatic, fully automatic, or otherwise, will overheat and fail if fired indefinitely. This issue tends to present itself primarily with fully automatic fire. For example, the MG34 may have a calculated cyclic rate of 1200 rounds per minute, but is likely to overheat and fail in the space of one minute of continuous fire. Semi-automatic firearms may also overheat if continuously fired. Recoil plays a significant role in the time it takes to reacquire one's sight picture, ultimately reducing the effective rate of fire.

Automatic firearm types

Automatic firearms can be divided into six main categories: ; Automatic rifle: The standard type of

service rifle A service rifle (or standard-issue rifle) is a rifle a military issues to regular infantry. In modern militaries, this is typically a versatile and rugged battle rifle, assault rifle, or carbine suitable for use in nearly all environments. M ...

s in most modern militaries, usually capable of selective fire. Assault rifles are a specific type of select-fire rifle chambered in an intermediate cartridge and fed via a high-capacity detachable magazine. Battle rifles are similar, but chambered in a full-powered cartridge. ; Automatic shotgun: A type of

combat shotgun A combat shotgun is a shotgun issued by militaries for warfare. The earliest shotguns specifically designed for combat were the trench guns or trench shotguns issued in World War I. While limited in range, the multiple projectiles typically ...

capable of firing shotgun shells automatically, usually also semi-automatically. ;

Machine gun A machine gun is a fully automatic, rifled autoloading firearm designed for sustained direct fire with rifle cartridges. Other automatic firearms such as automatic shotguns and automatic rifles (including assault rifles and battle rifles ...

: A large group of heavier firearms used for suppressive automatic fire of rifle cartridges, usually attached to a mount or supported by a bipod. Depending on size, weight and role, machine guns are divided into heavy,

medium Medium may refer to: Science and technology Aviation * Medium bomber, a class of war plane * Tecma Medium, a French hang glider design Communication * Media (communication), tools used to store and deliver information or data * Medium ...

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...

machine guns. The ammunition is often belt-fed. ;

Submachine gun A submachine gun (SMG) is a magazine-fed, automatic carbine designed to fire handgun cartridges. The term "submachine gun" was coined by John T. Thompson, the inventor of the Thompson submachine gun, to describe its design concept as an autom ...

: An automatic, short rifle ( carbine) typically chambered for

pistol A pistol is a handgun, more specifically one with the chamber integral to its gun barrel, though in common usage the two terms are often used interchangeably. The English word was introduced in , when early handguns were produced in Europe, a ...

cartridges. Today seldom used in military contexts due to a rise in the use of body armor, they are commonly used by police forces and close protection units in many parts of the world. ; Personal defense weapon: A new breed of automatic firearms that combines the light weight and size of the submachine gun with the medium power caliber ammunition of the rifle, thus in practice creating a submachine gun with body armor penetration capability. ; Machine pistol: A handgun-style firearm, capable of fully automatic or burst fire. They are sometimes equipped with a foldable shoulder stock, to promote accuracy during automatic fire, creating similarities to their submachine gun counterparts. Some machine pistols are shaped similarly to semi-automatics (e.g., the Glock 18, Beretta 93R). As with SMGs, machine pistols fire pistol caliber cartridges (such as the 9mm,

.40 The .40 S&W is a rimless pistol cartridge developed jointly by American firearms manufacturers Smith & Wesson and Winchester in 1990. The .40 S&W was developed as a law enforcement cartridge designed to duplicate performance of the Federal B ...

.45 ACP The .45 ACP ( Automatic Colt Pistol) or .45 Auto (11.43×23mm) is a rimless straight-walled handgun cartridge designed by John Moses Browning in 1904, for use in his prototype Colt semi-automatic pistol. After successful military trials, it ...

etc.).

Burst mode

Burst Automatic is an Automatic Fire mode, it is typically used to limit the number of rounds fired, due to the inaccuracy of fully automatic fire. In the US M16/M4 platforms, the burst mode fires three rounds per trigger reset. The rifle will not fire again until the trigger is released and 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 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 three rounds only.

Regulation

Automatic weapons tend to be restricted to

military A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...

and

police The police are a Law enforcement organization, constituted body of Law enforcement officer, persons empowered by a State (polity), state, with the aim to law enforcement, enforce the law, to ensure the safety, health and possessions of citize ...

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 The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

, taxes and strict regulations affect the manufacture and sale of fully automatic firearms under the National Firearms Act of 1934 and the closing of the "machine gun" registry by the

Firearm Owners Protection Act The Firearm Owners' Protection Act (FOPA) of 1986 is a United States federal law that revised many provisions of the Gun Control Act of 1968. Federal firearms law reform Under the Gun Control Act of 1968, the Bureau of Alcohol, Tobacco and Fi ...

of 1986 (only previously registered automatic weapons may be purchased). 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 A revenue stamp, tax stamp, duty stamp or fiscal stamp is a (usually) adhesive label used to designate collected taxes or fees on documents, tobacco, alcoholic drinks, drugs and medicines, playing cards, hunting licenses, firearm registration ...

, which is the legal document allowing possession of an automatic firearm. The use of a gun trust to register with the ATF has become an increasingly popular method of acquisition and ownership of automatic firearms.

Similar weapons

Other similar weapons not usually referred to as automatic firearms include the following: *

Autocannon An autocannon, automatic cannon or machine cannon is a fully automatic gun that is capable of rapid-firing large-caliber ( or more) armour-piercing, explosive or incendiary shells, as opposed to the smaller-caliber kinetic projectiles (bul ...

, which are 15 mm or greater in bore diameter and thus considered cannons, not small arms. *

Gatling gun The Gatling gun is a rapid-firing multiple-barrel firearm invented in 1861 by Richard Jordan Gatling. It is an early machine gun and a forerunner of the modern electric motor-driven rotary cannon. The Gatling gun's operation centered on a c ...

s, multiple-barrel designs, often used with external power supplies to generate rates of fire higher than automatic firearms.

References

{{Reflist Firearm actions *