A firearm is a device that can be used as a weapon that fires either single or multiple projectiles propelled at high velocity by the gases produced through rapid, confined burning of a propellant. This process of rapid burning is technically known as deflagration. In older firearms, this propellant was typically black powder, but modern firearms use smokeless powder, cordite, 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.
The term gun is often used as a synonym for firearm, but in specialist use has a restricted sense—referring only to an artillery piece with a relatively high muzzle velocity, such as a field gun, a tank gun, an anti-tank gun, or a gun used in the delivery of naval gunfire. Guns are distinct from howitzers and mortars, which have lower muzzle velocities and, typically, higher trajectories. Hand-held firearms, like rifles, carbines, pistols and other small firearms are rarely called "guns" in the restricted sense among specialists. Machine guns fire small caliber ammunition (generally 14.5 mm or smaller), and many machine guns are crew served firearms, requiring the services of more than one crewman, just like artillery guns. Generally, an automatic firearm designed for a single user is referred to as an automatic rifle. However, the US BATFE considers any firearm which dispenses more than one round with a single manipulation of the firing device to be a "machine gun" for regulatory purposes. Other terms, including "firearm" itself, have been defined in specialized ad hoc ways by various legislation.
In recent centuries, firearms have become the predominant weapons used by mankind. Modern warfare since the late Renaissance has relied upon firearms, with wide-ranging effects on military history and history in general. This created a whole new kind of battle, which molded modern-era armies.
For handguns and long guns, the projectile is a bullet or, in historical cannons, a cannonball. The projectile is fired by the burning of the propellant, but in small arms rarely contains explosives itself. For modern artillery the projectile is a shell, which nearly always contains explosives.
A distinction is sometimes made 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 virtually always a secondary method of attack. For example, arms such as rifles, muskets, and occasionally submachine guns can have bayonets affixed to them, becoming in effect a spear or pike. With some notable exceptions, the stock of a long gun can be used as a club. It is also possible to strike someone with the barrel of a hand-held gun or grasp it by the barrel and strike someone with the butt. This is called "pistol-whipping".
A problem for firearms is the accumulation of waste products from the partial combustion of propellants, metallic residue from the bullet itself, and small flecks of the cartridge case. These waste products can interfere with the internal functions of the firearm. As a result, regularly used firearms must be periodically partially disassembled, cleaned and lubricated to ensure the firearm’s reliability.
Firearms are sometimes referred to as small arms. Small arms are firearms which can be carried by a single individual. According to international conventions governing the Laws of War, small arms are defined (with some exceptions) as firearms which fire a projectile not in excess of 15 mm (0.60 inches) in diameter.citation needed] Small arms are aimed visually at their targets by hand using optical sights. The range of accuracy for small arms is generally limited to about one mile (1600 m), usually considerably less, although the current record for a successful Sniper attack is slightly more than 1.5 miles (2.4 km). Artillery guns are much larger than these firearms, mounted on a movable carriage, having bores of up to 18 inches (46 cm) and possibly weighing many tons. Artillery can be accurate at ranges of up to about 26 miles (42 km) and, with some notable exceptions (e.g., tank guns), are aimed using altitude/azimuth settings. Strictly speaking, such weapons are not firearms.