Sharps Bros. AR-15 Billet Stripped Upper Receiver w/Forward Assist 7075-T6 Aluminum Black Anodized. lower receivers perfectly and has a mil-spec front end that is compatible with any AR15 barrel nut and any AR15 handguard out there including those with rear facing tabs. This receiver is meant for .223 5.56 .224 Valkyrie 300 BLK and 6.5 Grendel calibers. Port opening is not large enough for 450 Bushmaster 458 SOCOM or 50 Beowulf. Made from 7075-T6 just like Sharps Bros. lower receivers. Anodized black. Comes with forward assist kit and dust cover installed. Specifications for Sharps Bros. AR-15 Billet Stripped Upper Receiver w/Forward Assist: Manufacturer: Sharps Bros. Color: Black Finish: Black Anodized Fabric/Material: 7075-T6 Aluminum Caliber: 6.5mm Grendel .224 Valkyrie .300 AAC Blackout Gun Make: AR Platform Gun Model: AR-15 Condition: New Projectile Caliber: .223 Caliber Features of Sharps Bros. AR-15 Billet Stripped Upper Receiver w/Forward Assist Comes with forward assist kit and dust cover installed. ''SHARPS BROS.'' discretely engraved on both sides. Package Contents: Sharps Bros. AR-15 Billet Stripped Upper Receiver w/Forward Assist What firearm models does the manufacturer say Sharps Bros. AR-15 Billet Stripped Upper Receiver w/Forward Assist is compatible with? The manufacturer says that Sharps Bros. AR-15 Billet Stripped Upper Receiver w/Forward Assist is compatible with AR-15Sharps Bros. SBUR04: AR-15 Billet Stripped Upper Receiver w/Forward Assist 7075-T6 Aluminum Black Anodized