Availability: In Stock
The CMMG AR-15 Resolute 100 Mk4 upper receiver assembly in .300 AAC Blackout gives you a complete, ready-to-run upper that pairs with any standard AR-15 lower receiver. Built for shooters who want suppressed, subsonic performance without compromise—whether that's hunting, home defense, or precision target work—this upper ships fully assembled with a zeroed bolt carrier group, charging handle, and muzzle brake already in place. No additional gunsmithing needed; bolt it onto your lower and you're running.
The 16-inch 4140CM barrel is twist-rated 1:7 to stabilize the heavy subsonic rounds that make .300 Blackout such a versatile platform, while the direct impingement gas system with carbine-length port and fixed 0.750-inch gas block keeps cycling predictable across both subsonic and supersonic loads. The billet 6061 T6 aluminum upper and CMMG EML15 M-LOK handguard provide a rock-solid foundation for mounting optics, lights, or tactical accessories, and the standard Cerakote finish is built to shrug off field use. At just over 4 pounds and 25 inches end-to-end, the Resolute 100 Mk4 balances shootability with the compact profile that makes .300 Blackout so appealing for short-range work and suppressed shooting in tight spaces.
This is a proven upper for the builder who doesn't want to source components individually or troubleshoot compatibility. CMMG has done the work—barrel, bolt carrier group, gas system, and controls are all factory-checked and matched. Grab a lower receiver and you've got a functional .300 Blackout rifle.
| Caliber | .300 AAC Blackout |
| Barrel Length | 16.1 inches |
| Barrel Twist | 1:7 |
| Barrel Material | 4140CM SBN |
| Barrel Contour | MT |
| Operating System | Direct Impingement |
| Gas Block | 0.750-inch non-adjustable |
| Gas Port Location | Carbine |
| Upper Receiver | Billet 6061 T6 aluminum |
| Handguard | CMMG EML15 M-LOK |
| Muzzle Device | CMMG ZEROED muzzle brake |
| Muzzle Thread | 5/8x24 |
| Charging Handle | CMMG ZEROED ambi |
| Finish | Cerakote (standard) |
| Overall Length | 25 inches |
| Weight | 4.1 lbs |
| Platform | Mk4 |
Yes. The Resolute 100 Mk4 is designed to pair with any standard AR-15 lower receiver. It's a drop-in upper, so assembly is straightforward—no special fitting or modifications required.
The upper ships complete and ready to fire. It includes the bolt carrier group (already installed), the CMMG ZEROED ambi charging handle, and the CMMG ZEROED muzzle brake. Polymer dust cover is also included. All components have been zeroed at the factory.
Yes. The barrel is threaded 5/8x24, the industry standard for .300 Blackout suppressors and other muzzle devices. The Resolute 100 was originally developed for suppressed and subsonic shooting, making it an excellent platform for that use. Note that you'll need to source your suppressor separately and comply with all applicable federal and local regulations.
The 1:7 barrel twist is optimized to stabilize both subsonic and supersonic .300 Blackout loads. Subsonic rounds (typically 220+ grain) are ideal for suppressed shooting and hunting in noise-sensitive areas, while supersonic loads (typically under 220 grain) deliver higher velocity and flatter trajectories for longer-range work. Both perform reliably in this platform.
SKU: 115789288 • Weight: 4.77oz
Availability: In Stock
The CMMG AR-15 Resolute 100 Mk4 upper receiver assembly in .300 AAC Blackout gives you a complete, ready-to-run upper that pairs with any standard AR-15 lower receiver. Built for shooters who want suppressed, subsonic performance without compromise—whether that's hunting, home defense, or precision target work—this upper ships fully assembled with a zeroed bolt carrier group, charging handle, and muzzle brake already in place. No additional gunsmithing needed; bolt it onto your lower and you're running.
The 16-inch 4140CM barrel is twist-rated 1:7 to stabilize the heavy subsonic rounds that make .300 Blackout such a versatile platform, while the direct impingement gas system with carbine-length port and fixed 0.750-inch gas block keeps cycling predictable across both subsonic and supersonic loads. The billet 6061 T6 aluminum upper and CMMG EML15 M-LOK handguard provide a rock-solid foundation for mounting optics, lights, or tactical accessories, and the standard Cerakote finish is built to shrug off field use. At just over 4 pounds and 25 inches end-to-end, the Resolute 100 Mk4 balances shootability with the compact profile that makes .300 Blackout so appealing for short-range work and suppressed shooting in tight spaces.
This is a proven upper for the builder who doesn't want to source components individually or troubleshoot compatibility. CMMG has done the work—barrel, bolt carrier group, gas system, and controls are all factory-checked and matched. Grab a lower receiver and you've got a functional .300 Blackout rifle.
| Caliber | .300 AAC Blackout |
| Barrel Length | 16.1 inches |
| Barrel Twist | 1:7 |
| Barrel Material | 4140CM SBN |
| Barrel Contour | MT |
| Operating System | Direct Impingement |
| Gas Block | 0.750-inch non-adjustable |
| Gas Port Location | Carbine |
| Upper Receiver | Billet 6061 T6 aluminum |
| Handguard | CMMG EML15 M-LOK |
| Muzzle Device | CMMG ZEROED muzzle brake |
| Muzzle Thread | 5/8x24 |
| Charging Handle | CMMG ZEROED ambi |
| Finish | Cerakote (standard) |
| Overall Length | 25 inches |
| Weight | 4.1 lbs |
| Platform | Mk4 |
Yes. The Resolute 100 Mk4 is designed to pair with any standard AR-15 lower receiver. It's a drop-in upper, so assembly is straightforward—no special fitting or modifications required.
The upper ships complete and ready to fire. It includes the bolt carrier group (already installed), the CMMG ZEROED ambi charging handle, and the CMMG ZEROED muzzle brake. Polymer dust cover is also included. All components have been zeroed at the factory.
Yes. The barrel is threaded 5/8x24, the industry standard for .300 Blackout suppressors and other muzzle devices. The Resolute 100 was originally developed for suppressed and subsonic shooting, making it an excellent platform for that use. Note that you'll need to source your suppressor separately and comply with all applicable federal and local regulations.
The 1:7 barrel twist is optimized to stabilize both subsonic and supersonic .300 Blackout loads. Subsonic rounds (typically 220+ grain) are ideal for suppressed shooting and hunting in noise-sensitive areas, while supersonic loads (typically under 220 grain) deliver higher velocity and flatter trajectories for longer-range work. Both perform reliably in this platform.
SKU: 115789288 • Weight: 4.77oz