CMMG Resolute Upper Receiver Group 5.7x28mm 16.1in Armor Black. Combine this RESOLUTE Upper Group with either our Mk57 Lower or a standard AR15 lower group and CMMGs 5.7 AR Conversion Magazines and youll be ready to hit the range Specifications for CMMG Resolute Upper Receiver Group: Manufacturer: CMMG Barrel Length: 16.1 in Muzzle Device: CMMG Zeroed Muzzle Brake Color: Armor Black Fabric/Material: 6061-T6 Aluminum Gun Rail: M-LOK Gun Type: Rifle Gun Make: AR Platform Gun Model: Universal Condition: New Magazine Included: No Mount Type: M-LOK Package Contents: CMMG Resolute Upper Receiver Group What firearm models does the manufacturer say CMMG Resolute Upper Receiver Group is compatible with? The manufacturer says that CMMG Resolute Upper Receiver Group is compatible with UniversalCMMG 57B40E4-AB: Resolute Upper Receiver Group 5.7x28mm 16.1in Armor Black