SilencerCo SCO15, Stripped Upper Receiver, .223 Remington/556NATO, Black AC5065 SilencerCo's AR-15 upper receiver is made from billet 7075-T6 aluminum" it is precision machined for compatibility with all of your preferred parts. With the SilencerCo billet AR-15 upper receiver" you get the materials" finish" and features you want and need to complete your dream AR-15 build.