Battle Arms Development Workhorse 16in 5.56 Nato Upper Receiver Assembly No Bcg No Ch. 56 NATO with a 1:7 twist M4 barrel extension and a Mid-length gas system. The barrel is finished with a .750" diameter low-profile gas block WORKHORSE 15in M-Lok Free Float Rail and an A2 flash hider. Upper: Forged 7075-T6 AR upper is hard coat anodized black for durability. Featuring M4 feed ramp cuts these upper receivers are made in specialized factories. This Upper Does Not Include BCG or Charging Handle Specifications for Battle Arms Development Workhorse 16in 5.56 Nato Upper Receiver: Manufacturer: Battle Arms Development Caliber: 5.56x45mm NATO Overall Length: 24.5 in Barrel Length: 16 in Barrel Profile: A2 Gas System Length: Mid Length Barrel Twist Rate: 1-7 Firearms Threads Per Inch: 1/2x28 Handguard Type: Free-Float Muzzle Device: A2 Flash Hider Finish: Nitride Fabric/Material: 4150 Chrome-Moly Vanadium Steel Gas Block Journal Size-Diameter: .750 in Handguard Length: 15 in Gun Rail: M-LOK Bolt Carrier Group Included: No Charging Handle Included: No Magazine Included: No Package Contents: Battle Arms Development Workhorse 16in 5.56 Nato Upper Receiver Battle Arms Development WH556-UA-16-223-BLK: Workhorse 16in 5.56 Nato Upper Receiver Assembly No Bcg No Ch