XTS Complete Upper Receiver w/o BCG w/ 12in Rail AR-15 223/5.56 24.75in 16.5in Carbine 1-8 Twist 1/2x28 Thread M-LOK Bird Cage Black Nitride Finish. 5in AR15 5.56 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 AR-15 16in 223/5.56 Complete Upper Receiver w/o BCG w/ 12in Rail: Manufacturer: XTS Caliber: .223 Remington Overall Length: 24.75 in Barrel Length: 16.5 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 Condition: New Fabric/Material: Stainless Steel Gas Block Journal Size-Diameter: .750 in Handguard Length: 12 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: 29.6 oz Magazine Included: No Mount Type: M-LOK Country of Origin: USA Package Contents: XTS AR-15 16in 223/5.56 Complete Upper Receiver w/o BCG w/ 12in Rail Anachor Upper Receiver 5.56 NATO Barrel 16.5in XTS Charging Handle XTS Forward Assist XTS Ejection Port Cover 12in M-LOK Black Gas Block Gas Tube Bird Cage Muzzle Brake What firearm models does the manufacturer say XTS AR-15 16in 223/5.56 Complete Upper Receiver w/o BCG w/ 12in Rail is compatible with? The manufacturer says that XTS AR-15 16in 223/5.56 Complete Upper Receiver w/o BCG w/ 12in Rail is compatible with AR-15XTS XTS-CU-12BK: Complete Upper Receiver w/o BCG w/ 12in Rail AR-15 223/5.56 24.75in 16.5in Carbine Length 1-8 Twist 1/2x28 Thread M-LOK Handguard Bird Cage Black Nitride Finish Black