The AR-15 chrome bolt group assembly is machined from 8620 carbon steel, that is heat treated. Exterior of carrier is chromed and interior is chrome-lined. Uses a Mil-Spec gas key that is chromed on the exterior, chrome-lined on the interior, heat treated and secured to the carrier with Grade 8 fasteners that are properly staked. The bolt assembly is machined from Carpenter No. 158® steel, has a tool steel extractor that is machined from bar stock and is chromed on the exterior.