The Maxim Defense MDX508 upper receiver is now available as a direct upgrade to your existing Mil-Spec lower receiver. It features an 8.5" barrel making it ideal for close-quarters situations. The included HATEBRAKE increases reliability and is tucked under the 9.5" handguard. These upper receiver groups ship complete, including a Maxim Defense Mil-Spec or SCW bolt carrier group, Radian Raptor charging handle, and Maxim Defense hand stop, ready to shoot right out of the box. Features Increased reliability due to included HATEBRAKE Armorer level adjustable gas block