XTS Complete Upper Receiver w/o BCG AR-15 300 BO 17.5in 8.5in Pistol 1-8 Twist 5/8x24 Thread M-LOK Bird Cage Black Nitride Finish. 5in AR15 300 Blackout upper comes FULLY ASSEMBLED With an Anchor Harvey Upper and an XTS Hand Guard. These XTS complete uppers do not include the Bolt Carrier Group. Specifications for XTS AR-15 8.5in 300 BO Complete Upper Receiver w/o BCG: Manufacturer: XTS Caliber: .300 AAC Blackout Overall Length: 17.5 in Barrel Length: 8.5 in Gas System Length: Pistol Length Barrel Twist Rate: 1-8 Threads per Inch: 5/8x24 Muzzle Device: A2 Flash Hider Finish: Nitride Color: Black Gun Model: AR-15 Condition: New Fabric/Material: Stainless Steel Gas Block Journal Size-Diameter: .750 in Handguard Length: 7 in Handguard Style: Round Rail Gun Rail: M-LOK Gun Make: AR Platform Barrel Material: 4150 Chrome Moly Vanadium Bolt Carrier Group Included: No Charging Handle Included: MIL-SPEC Weight: 16 oz Magazine Included: No Mount Type: M-LOK Country of Origin: USA Package Contents: XTS AR-15 8.5in 300 BO Complete Upper Receiver w/o BCG Anachor Upper Receiver 5.56 NATO Barrel 8.5in XTS Charging Handle XTS Forward Assist XTS Ejection Port Cover 7in M-LOK Black Gas Block Gas Tube Bird Cage Muzzle Brake What firearm models does the manufacturer say XTS AR-15 8.5in 300 BO Complete Upper Receiver w/o BCG is compatible with? The manufacturer says that XTS AR-15 8.5in 300 BO Complete Upper Receiver w/o BCG is compatible with AR-15XTS XTSCU8300BK: Complete Upper Receiver w/o BCG AR-15 300 BO 17.5in 8.5in Pistol Length 1-8 Twist 5/8x24 Thread M-LOK Handguard Bird Cage Black Nitride Finish Black