AR-15 style semi-automatic rifle

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.

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 also been the weapon used in many of the largest mass shootings in the United States, and is often legally classified as an assault weapon. 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.

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.

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