A firearm is a kinetic energy weapon that fires either a single or multiple projectiles propelled at high velocity by the gases produced by action of the rapid confined burning of a propellant. This process of rapid burning is technically known as deflagration. In older firearms, this propellant was typically gunpowder, but modern firearms use smokeless powder or other propellants.
The term gun is often used as a synonym for firearm, but in specialist use has a restricted sense - referring only to smoothbore firearms, machine guns, and naval artillery, and thus excluding rifles.
In recent centuries, firearms are the predominant weaponry used by mankind. Modern warfare since the late Renaissance has relied upon firearms, with wide-ranging effects on military history and history in general.
For handguns, long guns and historical cannon the projectile is a bullet or cannonball, fired by the burning of the propellant, but it does not generally contain explosives itself. For modern artillery the projectile is a shell, containing explosives.
A distinction can be drawn between the projectile itself as the weapon, and the firearm as a weapons platform. In some cases the firearm can be used directly as a weapon without firing a projectile, although this is generally a secondary method of attack. For example, arms such as rifles, muskets, and occasionally submachine guns can have bayonets fixed to them, becoming in effect a spear or pike. The stock of a long gun can be used as a club. It is also possible to strike someone with the barrel of a handgun or grasp it by the barrel and strike someone with the butt. This is called "pistol whipping".
A distinctive problem is the accumulation within the weapon of waste products from the combustion of propellants, residue from the bullet itself, and small flecks of the cartridge case. These waste products can interfere with the internal functions of the weapon. As such, regularly used firearms must be periodically partially diassembled, cleaned and lubricated to ensure the weapon's reliability.
There are two basic categories of firearms: artillery and small arms. Small arms are generally smaller man-portable firearms, while artillery are larger firearms. Strictly speaking, not all small arms are firearms, but it is the most convenient category under which to group firearms other than artillery.
The smallest of all small arms is the handgun. Handguns with a fixed firing chamber are pistols. A common handgun design that lacks a fixed firing chamber is the revolver, which holds a number of firing chambers in a revolving cylinder.
Prior to the 19th century handguns were often single-shot, but with the invention of the revolver in 1818, handguns capable of holding multiple rounds became popular. Most modern handguns that hold multiple rounds are semi-automatic.
The derringer is a short barreled handgun, with one or two barrels, that must be manually reloaded after being fired. Single-shot duelling pistols were used primarily in the 18th and 19th centuries. Fully automatic machine pistols were a 20th century development. The term 'machine pistol' is often used synonymously with 'submachine gun.'
Handguns have a variety of purposes. Handguns are small and often concealable, and are thus the first choice for personal protection. In the military, handguns are usually used by those who don't need larger firearms such as general and staff officers, and also by those for whom there is no room for a full-sized rifle, such as armored vehicle and air crews. In this role, they often compete with the carbine. Outside the military world, handguns are the usual armament for police (in those jurisdictions where the police are usually armed) and, where legal, for private citizens while in public. Private citizens who go about in public armed usually carry concealed handguns, since an unconcealed weapon would attract undue attention and would be less secure. In the United States, the number of states which permit concealed carry has recently grown to over 35, and several states have well over 100,000 permit-holders. The concept of citizens carrying a concealed weapon for self-defense is a contentious political issue; see gun politics for more information.
Handguns are also used for various hunting and sporting purposes.
Most modern long guns are either rifles or shotguns. Historically, a long smoothbore firearm was known as a musket. A rifle has a rifled barrel that fires single bullets while a shotgun fires large packets of shot, a single slug, or a specialty round (tear gas, bolo, lead powder, etc). Rifles are often built for accuracy and long range, and are usually aimed, while shotguns are usually designed to quickly hit a moving target. Rifles have a small impact area but a long range and high accuracy, while shotguns have a larger impact area with less range and accuracy. However, the larger impact area can compensate for reduced accuracy, since shot spreads during flight.
In the civilian world, rifles and shotguns are commonly used for hunting and to defend a home or place of business. Usually land game are hunted with rifles (although shotguns can be used, deer hunting with a shotgun usually employs the use of buckshot) while birds are hunted with shotguns. Shotguns are preferred for defending a home or business due to their shorter range and lesser penetration of walls and other structures, which reduce the chances of harm due to stray rounds.
A machine gun is a large, fully automatic firearm used almost exclusively by the military for large scale functions. They are primarily defensive weapons, mainly because of the difficulty involved in moving and placing them, though light machine guns (such as the US military's M249 Squad Automatic Weapon) often are wielded by a single infantryman in a typical squad; they provide large volumes of fire typically used for suppression and cover. Machine guns can also be mounted on vehicles or in helicopters and in World War II, the Korean War and in some other theatres, were major offensive weapons in fighter aircraft.
A Machine Gun is defined by The National Firearms Act of 1934, United States code Title 26, Subtitle E, Chapter 53, Subchapter B, Part 1, § 5845 as:
"any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger. The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun, and any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person."
Purchases by civilians of machine guns manufactured after 1986 were banned in the United States by the Firearm Owners Protection Act (FOPA), passed in that year. Machine guns manufactured or imported prior to 1986 can still be legally transferred to civilians who pay a tax to the BATFE and pass a background investigation. In addition, transferable machine guns must have been registered with the BATFE prior to 1986. Machine Gun parts kits (which do not include a functional receiver) can be transferred without restriction.
Loading and Firing Mechanisms
The cannon is loaded with gunpowder and the cannonball through the muzzle, while a fuse is placed at the rear. This fuse is lighted, causing the gunpowder to ignite and propel the cannonball. Most cannons were land or ship-based guns, although hand cannons also existed. In military use, the standard cannon was tremendously powerful, while hand cannon was somewhat useless.
Muzzle-loading muskets were the first small arms developed. Invariably, the firearm was loaded through the muzzle with both gunpowder and the bullet (usually referred to as a "ball"). Muzzleloaders still exist today and have their respective enthusiasts. However, muzzleloaders have to be reloaded after every shot, and a skilled archer could fire multiple arrows faster than most early muskets could be reloaded and fired. This became less of a concern as technology progressed, and muzzleloaders became the standard armament of modern militaries by the 18th century. Before that point the military effectiveness of muzzleloaders was hindered by the low reloading speed and, in early times, the high risk the weapon still posed to the person firing it.
Matchlocks were the first and simplest firing mechanisms developed. With a matchlock, the powder is ignited with a lit piece of cord, known as a "match". The match is wedged into one end of an S shaped piece of steel, which is pivoted to bring the match down into the touch hole. After each firing, the match usually had to be relit.
The wheellock predates the flintlock. While cumbersome and overly complicated, the wheel lock was a great improvement over the matchlock in terms of both convenience and safety, since it eliminated the need to keep an object smouldering while handling loose gunpowder. It has an operation much like the other locks, except that there is a wheel (much like that seen on cigarette lighters) which is wound up with a key before use and which, when the trigger is pulled, spins against flint creating sparks that ignite the powder. It was an innovation over the matchlock, but was not widely adopted. It was supposedly invented by Leonardo da Vinci, the Italian Renaissance man.
The flintlock was a major innovation in firearms design. The spark used to ignite the gunpowder was no longer generated by a complex wheellock, but rather by a piece of flint set in the jaws of the hammer, which when released by the trigger struck a piece of steel (the frizzen) to create the sparks. The hammer had to be reset after each firing and the flint replaced periodically due to wear from striking the frizzen. (See also flintlock mechanism, snaphance, miquelet)
Percussion caps operate under the same basic principle as the flintlock, but are more compact and sophisticated. They are also safer, and contain the entire gunpowder explosion inside the weapon. All modern-made muzzleloaders (except those built around the flintlock or earlier types of ignition) use percussive caps. See also caplock mechanism.
A major innovation in firearms came when ammunition, previously coming as separate bullets and powder, was consolidated into a metal cartridge that consolidated the percussion cap, the powder, and the bullet into one package. Cartridges continue to this day to be the standard in modern firearms. In cartridge-firing firearms, a hammer or firing pin strikes the cartridge's percussive cap, igniting the gunpowder. The percussive cap is placed at the rear of the cartridge, either on the rim (in which case it is a rimfire cartridge to be fired in a rimfire weapon) or at the center of the back of the cartridge (in which case it is a centerfire cartridge). As a general rule, centerfire cartridges are more powerful.
Caseless cartridges have been invented: these hold the cartridge together with paper or some other substance that's destroyed when the weapon is fired, eliminating the problem of brass casings ejecting and littering the ground. They are still largely in development.
Most firearms are capable of loading cartridges directly into the breech. Some additionally or exclusively load from a magazine that holds multiple rounds. Generally, a magazine is a box or cylinder that is designed to be reusable. Some magazines, such as those of the Garand, are loaded by a clip, which is a device that looks like a rail holding the ammunition by a rim. But in most cases, a magazine and a clip are different in that the former's function is to feed ammunition into the firearm's breech, while the latter's is to "charge" a magazine with ammunition.
Repeating, Semiautomatic, and Automatic Weapons
A firearm that can load multiple rounds as the weapon is re-cocked is considered a repeating weapon. A firearm that automatically recocks and reloads the next round after each shot is considered a semi-automatic weapon. An automatic (or "fully automatic") weapon is one that automatically recocks, reloads, and refires as long as the trigger is held down. Many modern firearms have a selective-fire option, where the weapon can be set with a switch to semiautomatic or automatic firing modes. This feature can be altered--with the M16A2 and M16A4 variants of the M16 full automatic fire is not available, but a three-round burst is, while on nearly all selective-fire firearms, the safety (a mechanical device that blocks the trigger) is usually built into the selective-fire switch.
The first automatic weapons were machine guns, usually designed similar to a Gatling gun. Within time, the automatic firing mechanism could be miniaturized. Automatic rifles such as the Browning Automatic Rifle (often referred to as the BAR) were in common use during the early part of the 20th century while automatic weapons that fired pistol rounds, known as submachine guns, also became popular during this period.
Submachine guns (such as the infamous Thompson Submachine Gun) were originally the approximate size of carbines. Later on, submachine guns were miniaturized. The most popular submachine gun in the world is currently the Heckler und Koch MP5. However, it is designated as a "machine pistol" by its manufacturer (MP5 stands for Machine Pistol 5), a designation some reserve to firearms such as the MAC-10, which are the size and shape of pistols, unlike the MP5.
However, Nazi Germany brought the world's attention to what was to become the most widespread class of automatic weapon: the assault rifle. The assault rifle is usually smaller than a traditional rifle, but has selective fire. Soviet engineer Mikhail Kalashnikov quickly adapted the concept to the AK-47, which became the world's most popular assault rifle. The United States reacted differently. John Garand, the inventor of the rifle used by the US military during World War II, the M1 Garand, adapted the design to produce the M14. The significant recoil of the weapon when fired in full automatic mode was seen as a problem, and it was replaced with a more modern assault rifle, Eugene Stoner's AR-15. The military later designated it as the M-16.
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