American Tactical 450 Bushmaster Complete AR-15 Upper is drop in ready, upper receiver assembly features a forged aluminum Mil-Sport AR-15 pattern upper receiver with a 16" barrel with 1:24 button cut rifling and black nitride finish chambered for 450 Bushmaster. Completed with a 15" aluminum free floated key-mod rail system over a carbine length low profile DGIS gas system, A2 style compensator and black nitride finished bolt carrier group. Fits to any AR-15 pattern lower receiver. 100% Made in USA and Assembled in Summerville, SC.