The AR-15 is a lightweight, 5.56 mm, magazine-fed, semi-automatic rifle, with a rotating-lock bolt, actuated by direct impingement gas operation or long/short stroke piston operation. It is manufactured with the extensive use of aluminum alloys and synthetic materials.
The AR-15 was first built by ArmaLite as a selective fire rifle for the United States armed forces. Because of financial problems, ArmaLite sold the AR-15 design to Colt. The select-fire AR-15 entered the US military system as the M16 rifle. Colt then marketed the Colt AR-15 as a semi-automatic version of the M16 rifle for civilian sales in 1963. Although the name "AR-15" remains a Colt registered trademark, variants of the firearm are independently made, modified and sold under various names by multiple manufacturers.