<P> An AR - 15 style rifle is a lightweight semi-automatic rifle based on the Colt AR - 15 design . After Colt's patents expired in 1977, an expanded marketplace emerged with many manufacturers producing their own version of the AR - 15 design for commercial sale . They are referred to as modern sporting rifles by the National Shooting Sports Foundation, a firearms industry trade association, and by some manufacturers . Coverage of high - profile incidents where various versions of the rifle were involved often uses the shorthand AR - 15 . </P> <P> Since 2010, AR - 15 style rifles have become one of the "most beloved and most vilified rifles" in the United States, according to the New York Times . It has been promoted as "America's rifle" by the National Rifle Association . It has been used in many mass shootings in the United States . The Federal Assault Weapons Ban restricted the Colt AR - 15 and derivatives from 1994 - 2004, although it did not affect rifles with fewer features . There are an estimated 10 - 12 million in circulation in the United States . </P> <P> In 1956, ArmaLite designed a lightweight assault rifle for military use and designated it the ArmaLite Rifle - 15, or AR - 15 . Due to financial problems, and limitations in terms of manpower and production capacity, ArmaLite sold the design and the AR - 15 trademark to Colt's Manufacturing Company in 1959 . In 1964, Colt began selling its own version with an improved semi-automatic design known as the Colt AR - 15 . After Colt's patents expired in 1977, an active marketplace emerged for other manufacturers to produce and sell their own AR - 15 style rifles . </P>

How many ar 15 type rifles in america