The CMMG AR-15 Resolute 300 Mk4 upper receiver assembly in 6.5 Grendel is a complete, ready-to-run platform for hunters and shooters who want a flatter trajectory and efficient ballistics at medium to long range. Built on the proven Mk4 platform, it pairs a 16-inch stainless steel barrel with a direct impingement operating system and drops onto any standard AR-15 lower receiver—no additional builds or tuning required. This is a plug-and-play solution for guys looking to add a 6.5mm option to their existing AR setup without the guesswork.

What sets this upper apart is the completeness of the package. It comes fully assembled with a bolt carrier group, ZEROED ambi charging handle, ZEROED dust cover, and a 6.5mm muzzle brake already installed and included. The 16.1-inch barrel runs a 1:8 twist rate tuned for the caliber, paired with a non-adjustable 0.750 gas block positioned at rifle length. The billet 6061 T6 aluminum upper is available in six Cerakote finishes, giving you clean aesthetics without sacrificing durability. The M-LOK handguard offers modern mounting flexibility for lights, grips, and other accessories without the bulk or weight penalty.

At 4.3 pounds and 25 inches overall, this upper strikes a practical balance—light enough for extended shooting sessions or hunting days in the field, yet long enough to wring out the 6.5 Grendel's ballistic potential. Whether you're building a dedicated medium-range rifle, setting up a versatile semi-auto for hunting, or just exploring what this cartridge can do, the Resolute 300 Mk4 takes the assembly work out of the equation and gets you on target faster.

The CMMG AR-15 Resolute 300 Mk4 upper receiver assembly in 6.5 Grendel is a complete, ready-to-run platform for hunters and shooters who want a flatter trajectory and efficient ballistics at medium to long range. Built on the proven Mk4 platform, it pairs a 16-inch stainless steel barrel with a direct impingement operating system and drops onto any standard AR-15 lower receiver—no additional builds or tuning required. This is a plug-and-play solution for guys looking to add a 6.5mm option to their existing AR setup without the guesswork.

What sets this upper apart is the completeness of the package. It comes fully assembled with a bolt carrier group, ZEROED ambi charging handle, ZEROED dust cover, and a 6.5mm muzzle brake already installed and included. The 16.1-inch barrel runs a 1:8 twist rate tuned for the caliber, paired with a non-adjustable 0.750 gas block positioned at rifle length. The billet 6061 T6 aluminum upper is available in six Cerakote finishes, giving you clean aesthetics without sacrificing durability. The M-LOK handguard offers modern mounting flexibility for lights, grips, and other accessories without the bulk or weight penalty.

At 4.3 pounds and 25 inches overall, this upper strikes a practical balance—light enough for extended shooting sessions or hunting days in the field, yet long enough to wring out the 6.5 Grendel's ballistic potential. Whether you're building a dedicated medium-range rifle, setting up a versatile semi-auto for hunting, or just exploring what this cartridge can do, the Resolute 300 Mk4 takes the assembly work out of the equation and gets you on target faster.