Multi-Caliber, Mil-Spec, AR15 Lower Receiver, manufactured in the USA of a high-impact proprietary composite polymer. This state-of-the-art polymer allows for superior strength, and unmatched durability and is extremely lightweight only 4.3oz. The AR1 eXtreme is by far the strongest composite polymer lower on the market today. The key to any good project is the foundation and on an AR15, that is the lower receiver. The Ar1 eXtreme comes with a lifetime warranty; and of course, it’s Proudly American.