These American Tactical Import (ATI) Complete Upper receivers feature a 15" free-floating MLOK rail, Phosphate BCG, and 16" barrel. Perfect for a new AR-15 build, the ATI MilSport line is compatible with any MilSpec parts or lower receiver you wish to work with. You can drop this upper right onto a complete lower and get right to the shooting range if you wish; it ships with a low profile gas block, flash hider, charging handle, complete bolt carrier group, barrel, and upper receiver assembly fully assembled.