The Aero Precision XL Upper is forged from 7075-T6 aluminum and features an enlarged ejection port. The XL Upper Receiver is your best choice when you're planning a build to send big rounds down range. Features- Port door opening enlarged to enhance larger diameter brass ejection (.450 Bushmaster, .458 SOCOM, .50 Beowulf, etc.), laser marked "XL" designation on the upper receiver tang, .250 takedown pin holes, and laser engraved t-markings. Compatible with AR15 Lower receivers, AR15 Port Doors and Forward Assists. Works with standard AR15/M16 components. Includes port door and forward assist.