The Aero Precision AR-15 barreled upper receiver is built around the M4E1 Threaded upper receiver designed for use with standard barrel nuts. The receiver is forged from 7075-T6 aluminum and precision machined to M4E1 specs to ensure proper fit with Mil-Spec and aftermarket parts. It is matte black hardcoat anodized and features laser engraved T-marks on the upper picatinny rail. This 18” .223 Wylde barreled upper comes with the Atlas S-One M-LOK free float handguard that features improved ergonomics, and a lightweight design with scalloped picatinny top rail. It also features a slim 1.3" internal diameter with indexing grooves for a comfortable grip.