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CMMG
The CMMG BANSHEE MK4 300BLK 12.5" upper receiver group delivers everything you need to assemble a capable short-barreled .300 Blackout rifle without hunting down components from multiple suppliers. Built on the proven AR15 platform, this complete upper receiver group bundles a quality barrel, bolt carrier group, and matched accessories in one package—purpose-built for subsonic and supersonic shooting. The 12.5" configuration strikes a practical balance for close-quarters hunting, home defense, or precision rifle work where compact handling matters.
At its heart sits a 4140CM steel barrel with a 1:7 twist rate, threaded 5/8x24 and crowned with CMMG's ZEROED linear compensator to manage recoil and blast signature. The direct impingement system runs a pistol-length gas port with a fixed 0.750" gas block, engineered for reliable cycling with both heavy and light .300 Blackout ammunition. The billet 6061-T6 aluminum upper receiver pairs with an 11-inch EML M-LOK handguard that gives you mounting flexibility for optics, lights, and accessories without excessive weight.
Everything arrives ready to mount on a compatible lower receiver: the ZEROED ambidextrous charging handle, polymer dust cover, and carrier group are all included and zeroed from the factory. The Cerakote Standard finish resists corrosion in the field, and at 3.7 lbs, the upper keeps the rifle light enough for extended hunting days or tactical drills. Whether you're building your first short .300 or adding a dedicated upper to an existing lower, this group eliminates guesswork and gets you on target faster.
| Brand | CMMG |
| Model | BANSHEE MK4 |
| Caliber | .300 Blackout |
| Barrel Length | 12.5" |
| Barrel Material | 4140CM Steel |
| Barrel Twist | 1:7 |
| Barrel Contour | MR |
| Upper Receiver | Billet 6061-T6 Aluminum |
| Handguard | CMMG EML11 M-LOK |
| Operating System | Direct Impingement |
| Gas Port | Pistol Length |
| Gas Block | 0.750" Non-Adjustable |
| Muzzle Device | CMMG ZEROED Linear Compensator |
| Muzzle Thread | 5/8x24 |
| Charging Handle | CMMG ZEROED Ambidextrous |
| Weight | 3.7 lbs |
| Overall Length | 20.8" |
| Finish | Cerakote Standard (Black) |
| Included | Bolt Carrier Group, Dust Cover, Ambidextrous Charging Handle, Linear Compensator |
This is a standard AR15-pattern upper receiver group and will mate with any .300 Blackout–chambered AR15 lower receiver. You'll need a lower that's either already set up for .300 Blackout or a standard multi-caliber lower to complete your rifle.
This upper receiver group includes the barrel, bolt carrier group, charging handle, dust cover, and linear compensator. You'll need to source a compatible lower receiver, magazine, and stock or brace to finish the rifle. All precision components are factory-zeroed and ready to use.
The 12.5" barrel balances handling and versatility: it's short enough for close-quarters hunting and home defense, yet long enough to reliably cycle both subsonic and supersonic .300 Blackout loads with the pistol-length gas system. The 1:7 twist stabilizes a wide range of bullet weights commonly used in this caliber.
Yes. The muzzle threads are 5/8x24, which is standard for .30-caliber suppressors. The linear compensator can be easily removed and replaced with a suppressor-compatible muzzle device if you plan to run a suppressor.
CMMG
The CMMG BANSHEE MK4 300BLK 12.5" upper receiver group delivers everything you need to assemble a capable short-barreled .300 Blackout rifle without hunting down components from multiple suppliers. Built on the proven AR15 platform, this complete upper receiver group bundles a quality barrel, bolt carrier group, and matched accessories in one package—purpose-built for subsonic and supersonic shooting. The 12.5" configuration strikes a practical balance for close-quarters hunting, home defense, or precision rifle work where compact handling matters.
At its heart sits a 4140CM steel barrel with a 1:7 twist rate, threaded 5/8x24 and crowned with CMMG's ZEROED linear compensator to manage recoil and blast signature. The direct impingement system runs a pistol-length gas port with a fixed 0.750" gas block, engineered for reliable cycling with both heavy and light .300 Blackout ammunition. The billet 6061-T6 aluminum upper receiver pairs with an 11-inch EML M-LOK handguard that gives you mounting flexibility for optics, lights, and accessories without excessive weight.
Everything arrives ready to mount on a compatible lower receiver: the ZEROED ambidextrous charging handle, polymer dust cover, and carrier group are all included and zeroed from the factory. The Cerakote Standard finish resists corrosion in the field, and at 3.7 lbs, the upper keeps the rifle light enough for extended hunting days or tactical drills. Whether you're building your first short .300 or adding a dedicated upper to an existing lower, this group eliminates guesswork and gets you on target faster.
| Brand | CMMG |
| Model | BANSHEE MK4 |
| Caliber | .300 Blackout |
| Barrel Length | 12.5" |
| Barrel Material | 4140CM Steel |
| Barrel Twist | 1:7 |
| Barrel Contour | MR |
| Upper Receiver | Billet 6061-T6 Aluminum |
| Handguard | CMMG EML11 M-LOK |
| Operating System | Direct Impingement |
| Gas Port | Pistol Length |
| Gas Block | 0.750" Non-Adjustable |
| Muzzle Device | CMMG ZEROED Linear Compensator |
| Muzzle Thread | 5/8x24 |
| Charging Handle | CMMG ZEROED Ambidextrous |
| Weight | 3.7 lbs |
| Overall Length | 20.8" |
| Finish | Cerakote Standard (Black) |
| Included | Bolt Carrier Group, Dust Cover, Ambidextrous Charging Handle, Linear Compensator |
This is a standard AR15-pattern upper receiver group and will mate with any .300 Blackout–chambered AR15 lower receiver. You'll need a lower that's either already set up for .300 Blackout or a standard multi-caliber lower to complete your rifle.
This upper receiver group includes the barrel, bolt carrier group, charging handle, dust cover, and linear compensator. You'll need to source a compatible lower receiver, magazine, and stock or brace to finish the rifle. All precision components are factory-zeroed and ready to use.
The 12.5" barrel balances handling and versatility: it's short enough for close-quarters hunting and home defense, yet long enough to reliably cycle both subsonic and supersonic .300 Blackout loads with the pistol-length gas system. The 1:7 twist stabilizes a wide range of bullet weights commonly used in this caliber.
Yes. The muzzle threads are 5/8x24, which is standard for .30-caliber suppressors. The linear compensator can be easily removed and replaced with a suppressor-compatible muzzle device if you plan to run a suppressor.
