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Availability: In Stock
The CMMG Resolute MK4 300 Blackout upper receiver is a complete, ready-to-mount assembled upper built for shooters who want to run subsonic or supersonic rounds through a compact, modern platform. Chambered in 300 Blackout with a 16.1-inch barrel, this upper is ideal for shorter-range hunting, home defense, or suppressed shooting where the cartridge's ballistics shine. It ships without a bolt carrier group or charging handle, so you'll need to source those separately—a common arrangement that lets you choose components that match your build philosophy.
The barrel is a 4140CM steel tube with a 1:7 twist rate suitable for 300 Blackout's range of bullet weights, fitted with CMMG's A2 flash hider (1/2 x 28 threads) and paired with a non-adjustable mid-length gas block for straightforward, maintenance-free operation. The billet 6061 T6 aluminum upper receiver provides solid lockup and durability, while the CMMG EML15 M-LOK handguard offers a free-float design—meaning it doesn't contact the barrel—for consistency shot to shot. That separation is a genuine advantage if you're chasing accuracy or planning to add optics and accessories.
At 3.6 pounds and 25 inches overall, this upper strikes a practical balance between handling and velocity. The Armor Black Cerakote finish resists wear and corrosion through hard use. Whether you're assembling a quiet 300 Blackout host, a subsonic hunting rig, or a full-power short-range carbine, the Resolute MK4 delivers CMMG's no-nonsense engineering in a configuration that's ready to go once you add your BCG, charging handle, and lower receiver.
| Platform | AR-15 / Mk4 |
| Caliber | 300 Blackout |
| Operating System | Direct Impingement |
| Barrel Length | 16.1 inches |
| Barrel Twist | 1:7 |
| Barrel Material | 4140CM Steel, SBN |
| Barrel Contour | MT |
| Muzzle Device | CMMG A2 Flash Hider |
| Muzzle Thread | 1/2 x 28 |
| Gas Block | Non-Adjustable, 0.750 inch |
| Gas Port Location | Mid |
| Upper Receiver | Billet 6061 T6 Aluminum |
| Handguard | CMMG EML15 M-LOK, Free-Float |
| Finish | Armor Black Cerakote |
| Weight | 3.6 lbs |
| Overall Length | 25 inches |
| Included | Upper receiver, barrel, handguard, gas block, flash hider (no BCG or charging handle) |
The BCG (bolt carrier group) and charging handle are not included. You'll need to purchase these separately and install them before the upper is ready to fire.
Yes. This is a standard AR-platform upper receiver compatible with any AR-15 lower receiver. Simply remove your current upper and attach this one to your existing lower.
Yes. The CMMG EML15 M-LOK handguard is free-floating, meaning it does not contact the barrel. This design improves accuracy consistency and allows for easier cleaning and maintenance.
The 1:7 twist barrel is designed to stabilize the broad range of 300 Blackout ammunition, including both subsonic and supersonic loads. Check your ammunition manufacturer's recommendations to ensure proper performance.
SKU: 194202099 • Weight: 5oz
Availability: In Stock
The CMMG Resolute MK4 300 Blackout upper receiver is a complete, ready-to-mount assembled upper built for shooters who want to run subsonic or supersonic rounds through a compact, modern platform. Chambered in 300 Blackout with a 16.1-inch barrel, this upper is ideal for shorter-range hunting, home defense, or suppressed shooting where the cartridge's ballistics shine. It ships without a bolt carrier group or charging handle, so you'll need to source those separately—a common arrangement that lets you choose components that match your build philosophy.
The barrel is a 4140CM steel tube with a 1:7 twist rate suitable for 300 Blackout's range of bullet weights, fitted with CMMG's A2 flash hider (1/2 x 28 threads) and paired with a non-adjustable mid-length gas block for straightforward, maintenance-free operation. The billet 6061 T6 aluminum upper receiver provides solid lockup and durability, while the CMMG EML15 M-LOK handguard offers a free-float design—meaning it doesn't contact the barrel—for consistency shot to shot. That separation is a genuine advantage if you're chasing accuracy or planning to add optics and accessories.
At 3.6 pounds and 25 inches overall, this upper strikes a practical balance between handling and velocity. The Armor Black Cerakote finish resists wear and corrosion through hard use. Whether you're assembling a quiet 300 Blackout host, a subsonic hunting rig, or a full-power short-range carbine, the Resolute MK4 delivers CMMG's no-nonsense engineering in a configuration that's ready to go once you add your BCG, charging handle, and lower receiver.
| Platform | AR-15 / Mk4 |
| Caliber | 300 Blackout |
| Operating System | Direct Impingement |
| Barrel Length | 16.1 inches |
| Barrel Twist | 1:7 |
| Barrel Material | 4140CM Steel, SBN |
| Barrel Contour | MT |
| Muzzle Device | CMMG A2 Flash Hider |
| Muzzle Thread | 1/2 x 28 |
| Gas Block | Non-Adjustable, 0.750 inch |
| Gas Port Location | Mid |
| Upper Receiver | Billet 6061 T6 Aluminum |
| Handguard | CMMG EML15 M-LOK, Free-Float |
| Finish | Armor Black Cerakote |
| Weight | 3.6 lbs |
| Overall Length | 25 inches |
| Included | Upper receiver, barrel, handguard, gas block, flash hider (no BCG or charging handle) |
The BCG (bolt carrier group) and charging handle are not included. You'll need to purchase these separately and install them before the upper is ready to fire.
Yes. This is a standard AR-platform upper receiver compatible with any AR-15 lower receiver. Simply remove your current upper and attach this one to your existing lower.
Yes. The CMMG EML15 M-LOK handguard is free-floating, meaning it does not contact the barrel. This design improves accuracy consistency and allows for easier cleaning and maintenance.
The 1:7 twist barrel is designed to stabilize the broad range of 300 Blackout ammunition, including both subsonic and supersonic loads. Check your ammunition manufacturer's recommendations to ensure proper performance.
SKU: 194202099 • Weight: 5oz