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A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and used by an individual.^[1][2][3] The term is legally defined further in different countries (see Legal definitions).

The first firearms originated in 10th-century China, when bamboo tubes containing gunpowder and pellet projectiles were mounted on spears to make the portable fire lance,^[4] operable by a single person, which was later used effectively as a shock weapon in the siege of De'an in 1132. In the 13th century, fire lance barrels were replaced with metal tubes and transformed into the metal-barreled hand cannon.^[5] The technology gradually spread throughout Eurasia during the 14th century. Older firearms typically used black powder as a propellant, but modern firearms use smokeless powder or other propellants. Most modern firearms (with the notable exception of smoothbore shotguns) have rifled barrels to impart spin to the projectile for improved flight stability.

Modern firearms can be described by their caliber (i.e. bore diameter). For pistols and rifles this is given in millimeters or inches (e.g. 7.62mm or .308 in.), or in the case of shotguns by their gauge (e.g. 12 ga. and 20 ga.). They are also described by the type of action employed (e.g. muzzleloader, breechloader, lever, bolt, pump, revolver, semi-automatic, fully automatic, etc.), together with the usual means of deportment (i.e. hand-held or mechanical mounting). Further classification may make reference to the type of barrel used (i.e. rifled) and to the barrel length (e.g. 24 inches), to the firing mechanism (e.g. matchlock, wheellock, flintlock, or percussion lock), to the design's primary intended use (e.g. hunting rifle), or to the commonly accepted name for a particular variation (e.g. Gatling gun).

Shooters aim firearms at their targets with hand-eye coordination, using either iron sights or optical sights. The accurate range of pistols generally does not exceed 100 metres (110 yd; 330 ft), while most rifles are accurate to 500 metres (550 yd; 1,600 ft) using iron sights, or to longer ranges whilst using optical sights. (Firearm rounds may be dangerous or lethal well beyond their accurate range; the minimum distance for safety is much greater than the specified range for accuracy). Purpose-built sniper rifles and anti-materiel rifles are accurate to ranges of more than 2,000 metres (2,200 yd).

A firearm is a barreled ranged weapon that inflicts damage on targets by launching one or more projectiles driven by rapidly expanding high-pressure gas produced by exothermic combustion (deflagration) of a chemical propellant, historically black powder, now smokeless powder.^[1][2][3]

In the military, firearms are categorized into heavy and light weapons regarding their portability by infantry. Light firearms are those that can be readily carried by individual foot soldier, though they might still require more than one individual (crew-served) to achieve optimal operational capacity. Heavy firearms are those that are too large and heavy to be transported on foot, or too unstable against recoil, and thus require the support of a weapons platform (e.g. a fixed mount, wheeled carriage, vehicle, aircraft or water vessel) to be tactically mobile or useful.

The subset of light firearms that only use kinetic projectiles and are compact enough to be operated to full capacity by a single infantryman (individual-served) are also referred to as small arms. Such firearms include handguns such as pistols, revolvers, and derringers; and long guns such as rifles (and their subtypes), shotguns, submachine guns, and machine guns.^[6]

Among the world's arms manufacturers, the top firearms manufacturers are Browning, Remington, Colt, Ruger, Smith & Wesson, Savage, Mossberg (United States), Heckler & Koch, SIG Sauer, Walther (Germany), ČZUB (Czech Republic), Glock, Steyr Arms (Austria), FN Herstal (Belgium), Beretta (Italy), Norinco (China), Rostec, and Kalashnikov (Russia). Former top producers included the Springfield Armory (United States), the Royal Small Arms Factory (United Kingdom), Mauser (Germany), Steyr-Daimler-Puch (Austria), and Rock Island Armory under Armscor (Philippines).^{[citation needed]}

As of 2018^[update] the Small Arms Survey reported that there were over one billion firearms distributed globally, of which 857 million (about 85 percent) were in civilian hands.^[7][8] U.S. civilians alone account for 393 million (about 46 percent) of the worldwide total of civilian-held firearms.^[8] This amounts to "120.5 firearms for every 100 residents".^[8] The world's armed forces control about 133 million (about 13 percent) of the global total of small arms, of which over 43 percent belong to two countries: the Russian Federation (30.3 million) and China (27.5 million).^[7] Law enforcement agencies control about 23 million (about 2 percent) of the global total of small arms.^[7]

A handgun is, as defined generally and in many gun laws, a firearm that can be used with a single hand.^{[9][10][11][12]} They are the smallest of all firearms, and are common as sidearms, concealed carry weapons, or as backup weapons for self-defense.

Handguns can be categorized into two broad types: pistols, which have a single fixed firing chamber machined into the rear of the barrel, and are often loaded using magazines of varying capacities; revolvers, which have a number of firing chambers or "charge holes" in a revolving cylinder, each one loaded with a single cartridge or charge; and derringers, broadly defined as any handgun that is not a traditional pistol nor a revolver.

There are various types of the aforementioned handguns designed for different mechanisms or purposes, such as single-shot, manual repeating, semi-automatic, or automatic pistols; single-action, double-action, or double-action/single-action revolvers; and small, compact handguns for concealed carry such as pocket pistols and "Saturday night specials".

Examples of pistols include the Glock, Browning Hi-Power, M1911 pistol, Makarov pistol, Walther PP, Luger pistol, Mauser C96, and Beretta 92. Examples of revolvers include the Colt Single Action Army, Smith & Wesson Model 10, Colt Official Police, Colt Python, New Nambu M60, and Mateba Autorevolver. Examples of derringers include the Remington Model 95, FP-45 Liberator, and COP .357 Derringer.

A long gun is any firearm with a notably long barrel, typically a length of 10 to 30 inches (250 to 760 mm) (there are restrictions on minimum barrel length in many jurisdictions; maximum barrel length is usually a matter of practicality). Unlike a handgun, long guns are designed to be held and fired with both hands, while braced against either the hip or the shoulder for better stability. The receiver and trigger group is mounted into a stock made of wood, plastic, metal, or composite material, which has sections that form a foregrip, rear grip, and optionally (but typically) a shoulder mount called the butt. Early long arms, from the Renaissance up to the mid-19th century, were generally smoothbore firearms that fired one or more ball shot, called muskets or arquebus depending on caliber and firing mechanism. Since the 19th and 20th centuries, various types of long guns have been created for different purposes.

A rifle is a long gun that has riflings (spiral grooves) machined into the bore (inner) surface of its barrel, imparting a gyroscopically stabilizing spin to the bullets that it fires. A descendant of the musket, rifles produce a single point of impact with each firing with a long range and high accuracy. For this reason, as well as for their ubiquity, rifles are very popular among militaries as service rifles, police as accurate long-range alternatives to their traditional shotgun long guns, and civilians for hunting, shooting sports, and self-defense.

Many types of rifles exist owing to their wide adoption and versatility, ranging from mere barrel length differences as in short-barreled rifles and carbines, to classifications per the rifle's function and purpose as in semi-automatic rifles, automatic rifles and sniper rifles, to differences in the rifle's action as in bolt-action, lever-action, and break-action rifles.

Examples of rifles of various types include the Henry rifle, Winchester rifle, Lee–Enfield, Gewehr 98, M1 Garand, MAS-36 rifle, AKM, Ruger 10/22, Heckler & Koch G3, Remington Model 700, and Heckler & Koch HK417.

A shotgun is a long gun that has a predominantly smoothbore barrel—meaning it lacks rifling—designed to fire a number of shot pellets in each discharge. These shot pellet sizes commonly range between 2 mm #9 birdshot and 8.4 mm #00 (double-aught) buckshot, and produce a cluster of impact points with considerably less range and accuracy, since shot spreads during flight. Shotguns are also capable of firing single solid projectiles called slugs, or specialty (often "less lethal") munitions such as bean bags or tear gas to function as a riot gun or breaching rounds to function as a door breaching shotgun. Shotgun munitions, regardless of type, are packed into shotgun shells (cartridges designed specifically for shotguns) that are loaded into the shotgun for use; these shells are commonly loose and manually loaded one-by-one, though some shotguns accept magazines.

Shotguns share many qualities with rifles, such as both being descendants of early long guns such as the musket; both having bolt-action, lever-action, break-action, pump-action, semi-automatic, and automatic variants; and both being popular with militaries, police, and civilians for largely the same reasons. However, unlike rifles, shotguns are less favored in combat roles due to their low accuracy and limited effectiveness in modern warfare, with combat shotguns often only used for breaching or close-quarters combat and sometimes limited to underbarrel attachments such as the M26 Modular Accessory Shotgun System. Shotguns are still popular with civilians for the suitability of their shot spread in hunting, clay pigeon shooting, and home defense.

Double-barreled shotguns are break-action shotguns with two parallel barrels (horizontal side-by-side or vertical over-under), allowing two single shots that can be loaded and fired in quick succession.

Examples of shotguns include the Winchester Model 1897, Browning Auto-5, Ithaca 37, Remington Model 870, Mossberg 500, Benelli M4, Franchi SPAS-12, Atchisson AA-12, and Knight's Armament Company Masterkey.

A carbine is a long gun, usually a rifle, that has had its barrel shortened from its original length or is of a certain size smaller than standard rifles, but is still large enough to be considered a long gun. How considerable the difference is between a rifle and a carbine varies; for example, the standard Heckler & Koch G36's barrel has a length of 480 mm (18.9 in), the G36K carbine variant's barrel is 318 mm (12.5 in), and the G36C compact variant's barrel is 228 mm (9.0 in). Some carbines are also redesigned compared to their rifle counterparts, such as the aforementioned G36/G36K and G36C, or the AK-74 and AKS-74U. However, some carbines, such as the M1 carbine, are not a variant of any existing design and are their own firearm model. Carbines are regardless very similar to rifles and often have the same actions (single-shot, lever-action, bolt-action, semi-automatic, automatic, etc.). This similarity has given carbines the alternate name of short barreled rifle (SBR), though this more accurately describes a full-size rifle with a shortened carbine-style barrel for close-quarters use.

The small size of a carbine provides lower weight and better maneuverability, making them ideal for close-quarters combat and storage in compact areas. This makes them popular firearms among special forces and police tactical units alongside submachine guns, considerably so since the late 1990s due to the familiarity and better stopping power of carbines compared to submachine guns. They are also popular with (and were originally mostly intended for) military personnel in roles that are expected to engage in combat, but where a full-size rifle would be an impediment to the primary duties of that soldier (logistical personnel, airborne forces, military engineers, officers, etc.), though since the turn of the millennium these have been superseded to a degree in some roles by personal defense weapons. Carbines are also common among civilian firearm owners who have size, space, and power concerns similar to military and police users.

Examples of carbines include the Winchester Model 1892, Rifle No. 5 Mk I, SKS, M1 carbine, Ruger Mini-14, M4 carbine, and Kel-Tec SUB-2000.

An assault rifle is commonly defined as a selective-fire rifle chambered in an intermediate cartridge (such as 5.56×45mm NATO, 7.62×39mm, 5.45×39mm, and .300 AAC Blackout) and fed with a detachable magazine.^{[13][14][15][16][17]} Assault rifles are also usually smaller than full-sized rifles such as battle rifles.

Originating with the StG 44 produced by Nazi Germany during World War II, assault rifles have since become extremely popular among militaries and other armed groups due to their universal versatility, and they have made up the vast majority of standard-issue military service rifles since the mid-20th century. Various configurations of assault rifle exist, such as the bullpup, in which the firing grip is located in front of the breech instead of behind it.

Examples of assault rifles include the Kalashnikov rifles of Soviet and Russian origin (such as the AK-47, AKM, and AK-74), as well as the American M4 carbine and M16 rifle.

A battle rifle is commonly defined as a semi-automatic or selective-fire rifle that is larger or longer than an assault rifle and is chambered in a "full-power" cartridge (e.g. 7.62×51mm NATO, 7.92×57mm Mauser, 7.62×54mmR). The term originated as a retronym to differentiate older full-powered rifles of these configurations like the M1 Garand, from newer assault rifles using intermediate cartridges like the Heckler & Koch HK33, but it is sometimes used to describe similar modern rifles such as the FN SCAR.

Battle rifles serve similar purposes as assault rifles, as they both are usually employed by ground infantry for essentially the same purposes. However, some prefer battle rifles for their more powerful cartridge, despite the added recoil. Some designated marksman rifles are configured from battle rifles, such as the Mk 14 Enhanced Battle Rifle and United States Marine Corps Designated Marksman Rifle, both essentially heavily modified and modernized variants of the M14 rifle.

Examples of rifles considered to be battle rifles include the FG 42, Gewehr 43, FN FAL, Howa Type 64, and Desert Tech MDR.

A sniper rifle is, per widespread definition, a high-powered precision rifle, often bolt-action or semi-automatic, with an effective range farther than that of a standard rifle. Though any rifle in a sniper configuration (usually with a telescopic sight and bipod) can be considered a sniper rifle, most sniper rifles are purpose-built for their applications, or are variants of existing rifles that have been modified to function as sniper rifles, such as the Type 97 sniper rifle, which was essentially a standard Type 38 rifle that was modified to be lighter and come with a telescopic sight.

Related developments are anti-materiel rifles, high-caliber rifles designed to destroy enemy materiel such as vehicles, supplies, or hardware; anti-tank rifles, anti-materiel rifles that were designed specifically to combat early armoured fighting vehicles, but are now largely obsolete due to advances in vehicle armour; scout rifles, a broad class of rifles generally summed up as short, lightweight, portable sniper rifles; and designated marksman rifles, semi-automatic high-precision rifles, usually chambered in intermediate or full-power cartridges, that fill the range gap between sniper rifles and regular rifles and are designed for designated marksmen in squads.

Examples of sniper and scout rifles include the M40 rifle, Heckler & Koch PSG1, Walther WA 2000, Accuracy International AWM, M24 Sniper Weapon System, Steyr Scout, Sako TRG, and CheyTac Intervention. Examples of anti-materiel and anti-tank rifles include the Mauser Tankgewehr M1918, Boys anti-tank rifle, PTRS-41, Barrett M82, Gepárd anti-materiel rifle, and McMillan TAC-50. Examples of designated marksman rifles include the SVD, SR-25, Dragunov SVU, Marine Scout Sniper Rifle, Mk 14 Enhanced Battle Rifle, and M110 Semi-Automatic Sniper System.

An automatic rifle is a magazine-fed rifle that is capable of automatic fire. They include most assault rifles and battle rifles, but originated as their own category of rifles capable of automatic fire, as opposed to the bolt-action and semi-automatic rifles commonly issued to infantry at the time of their invention. They usually have smaller magazine capacities than machine guns; the French Chauchat had a 20-round box magazine, while the Hotchkiss Mle 1914 machine gun, the French Army's standard machine gun at the time, was fed by a 250-round ammunition belt.

Though automatic rifles are sometimes considered to be their own category, they are also occasionally considered to be other types of firearms that postdated their invention, usually as light machine guns. Automatic rifles are sometimes confused with machine guns or vice versa, or are defined as such by law; the National Firearms Act and Firearm Owners Protection Act define a "machine gun" in United States Code Title 26, Subtitle E, Chapter 53, Subchapter B, Part 1, § 5845 as "... any firearm which shoots ... automatically more than one shot, without manual reloading, by a single function of the trigger". "Machine gun" is therefore largely synonymous with "automatic weapon" in American civilian parlance, covering all automatic firearms. In most jurisdictions, automatic rifles, as well as automatic firearms in general, are prohibited from civilian purchase or are at least heavily restricted; in the U.S. for instance, most automatic rifles are Title II weapons that require certain licenses and are greatly regulated.

Examples of automatic rifles include the Cei-Rigotti, Lewis gun, Fedorov Avtomat, and M1918 Browning Automatic Rifle.

A machine gun is a fully-automatic firearm, chambered in intermediate or full-power rifle cartridges, designed to provide sustained automatic direct fire as opposed to the semi-automatic or burst fire of standard rifles. They are commonly associated with being belt-fed, though many machine guns are also fed by box, drum, pan, or hopper magazines. They generally have a high rate of fire and a large ammunition capacity, and are often used for suppressive fire to support infantry advances or defend positions from enemy assaults. Owing to their versatility and firepower, they are also commonly installed on military vehicles and military aircraft, either as main or ancillary weapons. Many machine guns are individual-served and can be operated by a single soldier, though some are crew-served weapons that require a dedicated crew of soldiers to operate, usually between two and six soldiers depending on the machine gun's operation and the crew members' roles (ammunition bearers, spotters, etc.).

Machine guns can be divided into three categories: light machine guns, individual-served machine guns of an intermediate cartridge that are usually magazine-fed; medium machine guns, belt-fed machine guns of a full-power caliber and a certain weight that can be operated by an individual but tend to work best with a crew; and heavy machine guns, machine guns that are too large and heavy to be carried and are thus mounted to something (like a tripod or military vehicle), and require a crew to operate. A general-purpose machine gun combines these categories under a single flexible machine gun platform, often one that is most suitable as a light or medium machine gun but fares well as a heavy machine gun. A closely related concept is the squad automatic weapon, a portable light machine gun or even a modified rifle that is designed and fielded to provide a squad with rapid direct fire.

Examples of machine guns include the Maxim gun, M2 Browning, Bren light machine gun, MG 42, PK machine gun, FN MAG, M249 light machine gun, RPK, IWI Negev, and M134 Minigun.

A submachine gun is a magazine-fed carbine chambered in a small-caliber handgun cartridge (such as 9×19mm Parabellum, .45 ACP, .22 Long Rifle, and .40 S&W). They cannot be considered machine guns due to their small caliber, hence the prefix "sub-" to differentiate them from proper machine guns. Submachine guns are commonly associated with high rates of fire, automatic fire capabilities, and low recoil, though many submachine guns differentiate from this in various ways, such as having fairly low rates of fire or including burst and semi-automatic modes available through selective fire. Most submachine guns are the size of carbines and short-barreled rifles, and use similar configurations. Many are designed to take as little space as possible for use in close-quarters or for easy storage in vehicles and cases. Some submachine guns are designed and configured similar to pistols even down to size, and are thus occasionally classed as machine pistols, even if they are not actually a handgun (i.e. designed to require two hands to use).

Submachine guns are considered ideal for close-quarters combat and are cheap to mass-produce. They were very common in military service through much of the 20th century, but have since been superseded in most combat roles by rifles, carbines, and personal defense weapons due to their low effective range and poor penetration against most body armor developed since the late 20th century. However, they remain popular among special forces and police for their effectiveness in close-quarters and low likelihood to overpenetrate targets.

Examples of submachine guns include the MP 18, MP 40, Thompson submachine gun, M3 submachine gun, Uzi, Heckler & Koch MP5, Spectre M4, Steyr TMP, Heckler & Koch UMP, PP-2000, KRISS Vector, and SIG MPX.

A personal defense weapon is, in simplest terms, a submachine gun that is designed to fire ammunition with ballistic performance that is similar to (but not actually a type of) rifle cartridges, often called "sub-intermediate" cartridges. In this way, it combines the high automatic rate of fire, reliable low recoil, and lightweight compact maneuverability of submachine guns with the versatility, penetration, and effective range of rifles, effectively making them an "in-between" of submachine guns and carbines.

Personal defense weapons were developed to provide rear and "second-line" personnel not otherwise armed with high-caliber firearms (vehicle and weapon crews, engineers, logistical personnel, etc.) with a method of effective self-defense against skirmishers and infiltrators who cannot effectively be defeated by low-powered submachine guns and handguns, often the only firearms suitable for those personnel (while they could be issued rifles or carbines, those would become unnecessary burdens in their normal duties, during which the likelihood of hostility is fairly rare regardless, making their issuance questionable). Thus, per their name, personal defense weapons allow these personnel to effectively defend themselves from enemies and repel attacks themselves or at least until support can arrive. They are not intended for civilian self-defense due to their nature as automatic firearms (which are usually prohibited from civilian purchase), though some semi-automatic PDWs exist for the civilian market, albeit often with longer barrels.

Examples of personal defense weapons include the FN P90, Heckler & Koch MP7, AAC Honey Badger, and ST Kinetics CPW.

Types aside, firearms are also categorized by their "action", which describes their loading, firing, and unloading cycle.

Manual action or manual operation is essentially any type of firearm action that is loaded, and usually also fired, one cartridge at a time by the user, rather than automatically. Manual action firearms can be divided into two basic categories: single-shot firearms that can only be fired once per barrel before it must be reloaded or charged via an external mechanism or series of steps; and repeating firearms that can be fired multiple times per barrel, but can only be fired once with each subsequent pull of the trigger or ignite, and the firearm's action must be reloaded or charged via an internal mechanism between trigger pulls.

Types of manual actions include lever action, bolt action, and pump action.