CMMG AR-15 Resolute 300 Mk4 Upper Receiver Assembly - 6.5 Grendel, 16" Barrel, M-LOK HandguardCMMG$864.13
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CMMG
The CMMG AR-15 Resolute 300 Mk4 upper receiver assembly in 350 Legend gives you a purpose-built hunting upper that threads onto any standard AR-15 lower—no gunsmith required. If you're in a state where straight-walled cartridges are mandated for deer season, or you just want an effective, low-recoil hunting round, the 350 Legend delivers the velocity and energy you need without the kick of heavier calibers like .30-30 or .243 Win. This is a complete upper: bolt carrier group, charging handle, muzzle brake, and dust cover all come installed and zeroed from the factory.
The Mk4 platform pairs a 16.1" 4140CM barrel (1:16 twist) with a billet 6061-T6 aluminum upper receiver for rigidity and durability. The CMMG EML15 M-LOK handguard gives you modern accessory mounting without bulk, and the direct impingement gas system uses a carbine-length gas port and fixed 0.750" gas block for reliable cycling. The included ZEROED muzzle brake (1/2x28 thread) helps tame recoil and aids in spotting shots downrange. Whether you're assembling your first AR or adding a caliber-specific upper to your collection, this is a plug-and-play solution that arrives ready to hunt.
Available in multiple Cerakote finishes, the Mk4 Resolute 300 balances practical field ergonomics with clean aesthetics. It's lightweight at 4.0 lbs and measures 25" end-to-end, fitting standard shooting bags and truck racks. Pair it with a quality lower receiver, ammunition, and glass—and you'll have a versatile, accurate hunting rifle built to last.
| Brand | CMMG |
| Platform | Mk4 |
| Caliber | 350 Legend |
| Barrel Length | 16.1" |
| Barrel Twist | 1:16 |
| Barrel Material | 4140CM |
| Barrel Contour | MT |
| Operating System | Direct Impingement |
| Gas Port | Carbine Length |
| Gas Block | 0.750" Non-Adjustable |
| Upper Receiver | Billet 6061-T6 Aluminum |
| Handguard | CMMG EML15 M-LOK |
| Muzzle Device | CMMG ZEROED Muzzle Brake |
| Muzzle Thread | 1/2 x 28 |
| Charging Handle | CMMG ZEROED Ambi |
| Included Accessories | Bolt Carrier Group, Charging Handle, Muzzle Brake, Dust Cover (all factory installed and zeroed) |
| Weight | 4.0 lbs |
| Length | 25" |
| Finish | Cerakote Standard (multiple options available) |
The CMMG Resolute 300 Mk4 upper is designed to work with any standard AR-15 lower receiver, giving you flexibility in choosing your lower based on your budget and preferences.
Yes. The bolt carrier group, charging handle, muzzle brake, and dust cover are all factory installed. The accessories are factory zeroed, so you can mount it on a lower and begin setup without additional assembly or head-spacing concerns.
The 350 Legend was introduced as a straight-walled cartridge for hunters in states with caliber or cartridge restrictions—particularly common in Midwest deer seasons. It delivers effective power on target with noticeably less recoil than .30-30 or .243 Win, making follow-up shots easier and reducing fatigue during a hunting day.
No. This upper features a fixed 0.750" non-adjustable gas block tuned for reliable cycling with 350 Legend ammunition. The carbine-length gas port and direct impingement system are balanced for this caliber and configuration.
CMMG
The CMMG AR-15 Resolute 300 Mk4 upper receiver assembly in 350 Legend gives you a purpose-built hunting upper that threads onto any standard AR-15 lower—no gunsmith required. If you're in a state where straight-walled cartridges are mandated for deer season, or you just want an effective, low-recoil hunting round, the 350 Legend delivers the velocity and energy you need without the kick of heavier calibers like .30-30 or .243 Win. This is a complete upper: bolt carrier group, charging handle, muzzle brake, and dust cover all come installed and zeroed from the factory.
The Mk4 platform pairs a 16.1" 4140CM barrel (1:16 twist) with a billet 6061-T6 aluminum upper receiver for rigidity and durability. The CMMG EML15 M-LOK handguard gives you modern accessory mounting without bulk, and the direct impingement gas system uses a carbine-length gas port and fixed 0.750" gas block for reliable cycling. The included ZEROED muzzle brake (1/2x28 thread) helps tame recoil and aids in spotting shots downrange. Whether you're assembling your first AR or adding a caliber-specific upper to your collection, this is a plug-and-play solution that arrives ready to hunt.
Available in multiple Cerakote finishes, the Mk4 Resolute 300 balances practical field ergonomics with clean aesthetics. It's lightweight at 4.0 lbs and measures 25" end-to-end, fitting standard shooting bags and truck racks. Pair it with a quality lower receiver, ammunition, and glass—and you'll have a versatile, accurate hunting rifle built to last.
| Brand | CMMG |
| Platform | Mk4 |
| Caliber | 350 Legend |
| Barrel Length | 16.1" |
| Barrel Twist | 1:16 |
| Barrel Material | 4140CM |
| Barrel Contour | MT |
| Operating System | Direct Impingement |
| Gas Port | Carbine Length |
| Gas Block | 0.750" Non-Adjustable |
| Upper Receiver | Billet 6061-T6 Aluminum |
| Handguard | CMMG EML15 M-LOK |
| Muzzle Device | CMMG ZEROED Muzzle Brake |
| Muzzle Thread | 1/2 x 28 |
| Charging Handle | CMMG ZEROED Ambi |
| Included Accessories | Bolt Carrier Group, Charging Handle, Muzzle Brake, Dust Cover (all factory installed and zeroed) |
| Weight | 4.0 lbs |
| Length | 25" |
| Finish | Cerakote Standard (multiple options available) |
The CMMG Resolute 300 Mk4 upper is designed to work with any standard AR-15 lower receiver, giving you flexibility in choosing your lower based on your budget and preferences.
Yes. The bolt carrier group, charging handle, muzzle brake, and dust cover are all factory installed. The accessories are factory zeroed, so you can mount it on a lower and begin setup without additional assembly or head-spacing concerns.
The 350 Legend was introduced as a straight-walled cartridge for hunters in states with caliber or cartridge restrictions—particularly common in Midwest deer seasons. It delivers effective power on target with noticeably less recoil than .30-30 or .243 Win, making follow-up shots easier and reducing fatigue during a hunting day.
No. This upper features a fixed 0.750" non-adjustable gas block tuned for reliable cycling with 350 Legend ammunition. The carbine-length gas port and direct impingement system are balanced for this caliber and configuration.