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, unmatched durability and is extremely lightweight only 4.3 oz. 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. Features: Superior strength - built with proprietary composite polymer to withstand extreme conditions Unmatched durability - when most lowers dent or break the AR1 eXtreme bounces back to shape Extremely lightweight - 4.3 oz, accepts all standard Mil-Spec uppers up to .50 Beowulf Compatible with most current AR-15 lower parts kits, grips and stocks Unconditional lifetime warranty Custom engraving - "the tree of liberty must be refreshed from time to time with the blood of patriots and tyrants" 100% USA made High impact proprietary composite polymer