CMMG Resolute Mk4 Complete Upper Features The CMMG Resolute Mk4 was built to combine the familiar handling of the AR-15 platform with the added stopping power of .338 ARC a cartridge designed to emulate the sub and supersonic versatility of .300 Blackout while delivering more energy on target. A 16.1 inch barrel finished in black nitride uses a 1 in 8 twist rate a slower rate chosen specifically to stabilize more traditionally constructed .338 caliber projectiles rather than the fast twists common on smaller bore AR cartridges. CMMG threads a Zeroed muzzle brake onto the barrel a device tuned to work with the .338 ARC cartridge s recoil impulse and to transition well between suppressed and unsuppressed shooting. Notably .338 ARC shares the same bolt as 6.5 Grendel AR-15 builds so shooters already invested in that ecosystem gain an easier path to parts compatibility. The upper s aluminum receiver is finished in a black armor Cerakote a coating selected for its resistance to wear and corrosion under hard use conditions. An M-LOK handguard surrounds the barrel giving shooters the mounting real estate needed for lights optics mounts slings and other accessories without needing a separate rail adapter. CMMG designed .338 ARC specifically to require less gas system tuning than some large bore alternatives when switching between suppressed and unsuppressed configurations simplifying life for shooters who run a can. For AR-15 owners looking to add genuine big bore performance to an existing lower without building an entirely new rifle the Resolute Mk4 upper offers a direct well engineered path to do exactly that. CMMG Resolute Mk4 Complete Upper Specifications Manufacturer: CMMG Model: Resolute Mk4 Caliber: .338 ARC Barrel Length: 16.1 Barrel Finish: Black Nitride Twist Rate: 1:8 Muzzle Device: CMMG Zeroed Muzzle Brake Handguard: M-LOK Receiver Material: Aluminum Receiver Finish: Black Armor Cerakote Muzzle Thread: 5/8x24 Weight: 4.1 lbs Available At: GrabAGun