M4E1 Enhanced Upper Receiver Stripped in Anodized Black. The M4E1 upper is a one-piece design that combines the handguard mounting platform with the upper receiver, compressing the parts needed to mount a free-floated handguard to eight screws. Forged from 7075-T6 aluminum and finished in Anodized Black, this stripped upper will NOT ship with a barrel nut. It is compatible with standard AR-15/M16 components and supports Aero Precision Enhanced and Quantum Series handguards as well as most BAR-system handguards. Features M4 Feedramps and .250 takedown pin holes. M4E1 specific details include the forged handguard mounting platform, enhanced fitting, and compatibility with barrels up to 1" diameter.