USED CMMG Mk4/AR-15 Upper Receiver Assembly Armor Black 55BA290-AB. Available in six different Cerakote finishes this upper receiver omits the forward assist for those looking for a sleek and stylish base to start a new AR15 build. Specifications for CMMG Mk4/AR15 Upper Receiver Assembly: Manufacturer: CMMG Finish: Cerakote Fabric/Material: Forged 7075-T6 Aluminum Gun Make: CMMG AR Platform Gun Model: CMMG Mk4 AR-15 Magazine Included: No Package Contents: CMMG Mk4/AR15 Upper Receiver Assembly What firearm models does the manufacturer say CMMG Mk4/AR15 Upper Receiver Assembly is compatible with? The manufacturer says that CMMG Mk4/AR15 Upper Receiver Assembly is compatible with AR-15 CMMG Mk4CMMG 55BA290-AB: Mk4/AR-15 Upper Receiver Assembly Armor Black