The Sons of Liberty Gun Works AR-15 lower receivers are built from mil-spec 7075-T6 forgings from the lead forge in the U.S. The contour is fully machined leaving no flash marks from the forging. We take extra care when machining our lower receivers resulting in tolerances that are tighter and fits that are better than other lower receivers. We use mil-spec Matte black hard-coat anodized Mil 8625 Type 3 Class 2 finish.