CMMG MK4 Upper Receiver Assembly Features The CMMG MK4 Upper Receiver Assembly is machined from billet 6061-T6 aircraft-grade aluminum a material selected for its exceptional strength-to-weight ratio and dimensional stability that ensures precise fitment with mil-spec AR-15 lower receivers and component interfaces while maintaining the rigidity needed for accurate and reliable long-term operation. The billet construction allows for tighter tolerances and more refined external geometry compared to forged upper receivers giving builders a premium aesthetic and a precisely machined foundation that elevates the overall quality of a custom AR-15 build from the ground up. For AR-15 builders who want a billet aluminum upper receiver with aircraft-grade material quality and CMMG s established manufacturing standards as the foundation of their next build the MK4 Upper Receiver Assembly provides exactly that starting point. The CMMG MK4 Upper Receiver Assembly comes with the ZEROED Polymer Dust Cover pre-installed eliminating one of the fiddly small-parts installation steps common in AR-15 builds and allowing builders to move directly to barrel and handguard installation without sourcing and fitting a separate dust cover assembly. The deliberate omission of the forward assist gives this upper receiver a clean and streamlined profile that is increasingly popular among competition shooters minimalist builders and enthusiasts who prefer the aesthetic of a no-forward-assist upper without the added weight and visual complexity of the standard component. For AR-15 builders who want a pre-assembled billet 6061-T6 upper with a factory-installed dust cover and a clean no-forward-assist design in an Armor Black finish ready to accept a barrel handguard and bolt carrier group the CMMG MK4 Upper Receiver Assembly is available at GrabAGun. CMMG MK4 Upper Receiver Assembly Specifications Manufacturer: CMMG Model: MK4 Upper Receiver Assembly Type: Assembled Upper Receiver Platform: MK4/AR-15 Color: Black Material: Billet 6061-T6 Aircraft-Grade Aluminum Finish: Armor Black Forward Assist: None Dust Cover: ZEROED Polymer Pre-Installed Compatible Hosts: AR-15 Available At: GrabAGun