XTS Complete Upper Receiver w/o BCG w/ 12in Ce Rail USA Edition AR-15 24.75in 16in Barrel Carbine 1-8 Twist 1/2x28 Thread M-LOK Stainless Steel Bird. 56 upper comes FULLY ASSEMBLED with a 5.56 NATO barrel capable of shooting both .223 and 5.56. These XTS complete uppers do not include the Bolt Carrier Group. Specifications for XTS USA Edition AR-15 .223/5.56 Complete Upper w/o BCG w/ 12in Ce Rail: Manufacturer: XTS Caliber: .223 Remington Overall Length: 24.75 in Gas System Length: Carbine Length Barrel Twist Rate: 1-8 Threads per Inch: 1/2x28 Muzzle Device: A2 Flash Hider Finish: Nitride Color: Black Gun Model: AR-15 Fabric/Material: Stainless Steel Gas Block Journal Size-Diameter: .750 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 Magazine Included: No Mount Type: M-LOK Country of Origin: USA Package Contents: XTS USA Edition AR-15 .223/5.56 Complete Upper w/o BCG w/ 12in Ce Rail Anchor Harvey Upper Receiver 300 b/o Barrel XTS Charging Handle XTS Forward Assist XTS Ejection Port Cover 7? M-LOK RAIL Black Gas Block Gas Tube Bird Cage Muzzle Brake What firearm models does the manufacturer say XTS USA Edition AR-15 .223/5.56 Complete Upper w/o BCG w/ 12in Ce Rail is compatible with? The manufacturer says that XTS USA Edition AR-15 .223/5.56 Complete Upper w/o BCG w/ 12in Ce Rail is compatible with AR-15XTS XTS-CU-16US: Complete Upper Receiver w/o BCG w/ 12in Ce Rail USA Edition AR-15 24.75in 16in Barrel Carbine Length 1-8 Twist 1/2x28 Thread M-LOK Handguard Stainless Steel Bird Cage Black Nitride Finish Black