Definition of Firearm

Legal Definition. Under 26 USCA § 861 (a), firearm is defined as “a shot gun or rifle having a barrel of less than eighteen inches in length, or any other weapon, except a pistol or revolver, from which a shot is discharged by an explosive if such weapon is capable of being concealed on the person, or a machine gun, and includes a muffler or silencer for any firearm whether or not such firearm is included within the foregoing definition." United States v. Adams, 11 F. Supp. 216, 217 (S.D. Fla. 1935).

A firearm projects either single or multiple projectiles at high velocity through rapid, confined burning of a propellant; a process technically known as deflagration. In older firearms, the propellant was typically black powder or cordite, but modern firearms use smokeless powder or other propellants.

Most weapons fall into one of four major categories: handguns (revolvers, semi-automatic guns, and submachine guns), and long guns (rifles and shotguns).    

The four major focuses of firearm technology are: projectile accuracy, increasing the force delivered by the projectile, increasing the rate of firing, and improving the reliability of the firing mechanism.