Aero Precision M5 Assembled Upper, For AR10, Anodized, Flat Dark Earth APAR308505AC 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 Aero's M5 .308 lower receiver for a solid and dependable fit.