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No its high tech plastic
Multi-Caliber, Mil-Spec, AR15 Lower Receiver, manufactured in the USA of a high impact proprietary composite polymer

Nope, high speed plastic it is.

Hi Damon, this is not aluminum. Made from space age materials, the AR1 eXtreme lower is made from an impact resistant polymer blend selected specifically for the construction of firearms. The lower is so strong it can be used with any mil-spec upper chambered in everything from .22lr all the way up to the powerful .50 Beowulf. Specifications and Features: - FMK Firearms AR1 eXtreme - R15 Stripped Lower AR1EXTREME - 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 - Accepts all standard MIL SPEC uppers up to .50 Beowulf - Compatible with most current AR15 lower parts kits, grips and stocks - Unconditional lifetime warranty - High Impact Proprietary Composite Polymer Frame - Multi-Caliber - Mil-Spec - Overall Weight 4.3oz - 100% USA Made - Matte Black.