The thin and comfortable Diamondhead VRS Free Float Forend feels just as good as it looks on this .300 Blackout Caliber Windham Weaponry Flattop Upper Receiver Assembly. The complete Assembly includes a 16” Medium Profile Barrel with Bolt and Bolt Carrier. The Barrel is 4150M Chrome Moly Vanadium 11595E Steel, Chrome Lined in Bore and Chamber, rifled 1 turn in 7 inches – right hand twist. A Low Profile Gas Block is in place under the forend assembly, and the muzzle is fitted with a Diamondhead “T” Brake. A Push Button Q.D. Sling Swivel is also included. The MIL-STD 1913 Top Rail is on the same plane as the Upper Receiver Rail. The flat top type Upper Receiver is CNC machined from 7075T6 aircraft grade aluminum, hard coat black anodized to mil spec. This assembly is ready to attach to your lower receiver assembly and take to the range. The .300 Blackout Caliber ammunition will function in .223 / 5.56mm magazines, but for safety’s sake do not mix up the two ammunitions – which is why we Laser Engrave the Upper as .300 Blackout Caliber. Chambering incorrect ammunition in your upper could cause catastrophic damage or injury. Always use factory ammunition that corresponds to the stampings on your barrel.