The billet-ar upper receiver set is 100% machined in the usa and was engineered from the ground up to address structural design weaknesses in standard usgi receivers and enhance overall tolerances.It has a precise bolt raceway for smoother chambering, more rigid receiver walls to reduce firing flex.The billet-ar upper receiver is cnc machined from 7075-t6 aerospace aluminum billet stock with a top picatinny rail, m4-style extended feed ramps, and smooth side profile without forward assist for maximum accuracy potential.Receiver Finish: Black Hard Coat AnodizedType: Upper ReceiverCaliber: 223 RemSights: None, Optic ReadyReceiver Description: 7075-T6 Aluminum