Built to the correct Mil-Specs. (Inside Diameter for barrel extension slightly undersized for a tighter fit to the barrel and a more accurate rifle.)Features• Precision machined to correct Mil-Specs from 7075 T6 Forgings • Fully Assembled with forward assist, and ejection port cover • Mil-Std 1913 Rail for mounting optics and accessories • Machined for use with barrels that use an M4 barrel extension • Laser etched T-markings for addressing the remounting of optics • Includes Mil-Spec Forward Assist with heat treated tool steel pawl, with press fit and pinned cap • Hard Coat Anodized per Mil-A-8625F, Type III, Class2 • Dry Film Lube on interior bore per Mil-Specs • Made in the U.S.A. This product will not include the BCM logo etched on the receiver. It is marked "BCM4" over the gas tube hole.