The AR-15 reference article from the English Wikipedia on 24-Apr-2004
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AR-15

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The AR-15 is a self-loading rifle designed by Eugene Stoner of the Armalite corporation. It has been manufactured by various companies in both automatic and semiautomatic versions, in many configurations. A typical caliber for the AR-15 is the .223. Within the US military, the rifle is known by the military designation M16. Developed by Eugene Stoner after the AR-10 rifle, it preserved most of its predecessors admirable features, and was adopted in limited numbers by the US Air Force. The Military has recently selected and deployed the M-4, a carbine version of the M-16.

See M16 for more details.