Aero Precision M5, Assembled Upper Receiver, Anodized Finish, Olive Drab Green, Fits AR10 APAR308631AC The M5 .308 Assembled Upper Receiver comes with both the port door and forward assist hardware preinstalled. Forged from 7075-T6 aluminum" this assembled upper is precision machined to accept standard .308 components and is the perfect upper for your big bore build. Match this with their M5 .308 lower receiver for a solid and dependable fit.