Bushmaster AR-15 upper receiver assembly in 5.56x45 NATO with a 24" fluted extra heavy barrel featuring an 11 degree target crown. Custom match hybrid chamber for 5.56x45mm NATO and .223 Remington ammunition. 1:9 twist for optimal performance with a variety of bullet weights and ammunition. A vented free-float forend, a low profile gas block and B.M.A.S. mini risers make this perfect for installing your choice of scope or any other optic. Complete with bolt carrier group and charging handle.