Aero Precision M5 Assembled Upper, For AR10, Anodized, Black APAR308503AC 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.