A firearm is a portable gun, being a barreled weapon that launches one or more projectiles, such as a pistol or rifle. Firearms first appeared in 13th century China when the man portable fire lance (a bamboo or metal tube that could shoot ignited gunpowder) was combined with projectiles such as scrap metal, broken porcelain, or darts/arrows. The technology gradually spread through the rest of Asia and into Europe. In older firearms, the propellant was typically black powder, but modern firearms use smokeless powder or other propellants. Most modern firearms (with the notable exception of smoothbore firearms) have rifled barrels to impart spin to the projectile for improved flight stability.
Modern firearms are typically described by their bore diameter (75mm) or calibre (7.62mm) or gauge (12 ga.), the type of action employed (muzzle, breech, lever, bolt, revolver, semi-automatic, or automatic) together with the usual means of deportment (hand-held or mechanical mounting). They may be further distinguished by reference to the type of barrel used (rifled) and the barrel length (19 inch), the design's primary intended target (anti-aircraft), or the commonly accepted name for a particular variation (Gatling gun).
Firearms may sometimes be referred to as small arms when they are intended primarily for use by military forces if they can be carried by a single individual.
The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16 rifle, all based on the original AR-15 rifle designed by Eugene Stoner and made by ArmaLite. The M4 is a shorter and lighter variant of the M16A2 assault rifle, with 80% parts commonality.
It is a gas-operated, magazine-fed, selective fire, shoulder-fired weapon with a telescoping stock. A shortened variant of the M16A2 rifle, the M4 has a 14.5 in (370 mm) barrel, allowing its user to better operate in close quarters combat. Like the rest of the M16 family, it fires the .223 caliber, or 5.56mm NATO round. The M4 has selective fire options including semi-automatic and three-round burst (like the M16A2 and M16A4), while the M4A1 has the capability to fire fully automatic instead of three-round burst (like the M16A1 and M16A3). The carbine is also capable of mounting an M203 grenade launcher (the M203A1 with a 9-inch barrel as opposed to the standard 12-inch barrel of the M203 used on the M16 series) as well as its successor, the M320 grenade launcher.