The Complete Hydra® Upper Receiver Assembly chambered in .300 Blackout!  We started from the Hydra® Quick Change Barrel Upper Receiver (QCB-D) and added a whole lot more.  This Complete Upper Receiver includes a 16-inch .300 Blackout Barrel w/ Low Profile Gas Block in carbine length with Flash Hider, the Hydra® Modified Bolt Carrier with a 5.56 Bolt and Firing Pin and Charging Handle. Mlok rails included!