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. FeaturesIncreased reliability due to included HATEBRAKEArmorer level adjustable gas blockM-slot compatible handguardMilitary-grade materials [17-4 Stainless Steel, 7075 and 6061 Aluminum]HK height rail for a more rigid upper receiverInstalls on any Mil-Spec lower receiver