CMMG BANSHEE MK4 300BLK 12.5" Upper Receiver Group - Black

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.

Key Features

• Complete upper receiver group—barrel, bolt carrier, and charging handle included and factory-zeroed
• 12.5" 4140CM barrel with 1:7 twist for reliable .300 Blackout performance
• CMMG ZEROED linear compensator (5/8x24 muzzle threads)
• Direct impingement operating system with fixed gas block
• Billet 6061-T6 aluminum upper receiver for durability and accuracy
• 11-inch EML M-LOK handguard for easy accessory mounting
• Ambidextrous ZEROED charging handle for left and right-handed shooters
• Includes polymer dust cover
• Lightweight at 3.7 lbs; 20.8" overall length
• Cerakote Standard finish for field durability

Specifications

Frequently Asked Questions

What lower receivers are compatible with this upper group?

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.

Does this upper come with everything I need to assemble a 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.

What's the advantage of the 12.5" barrel for .300 Blackout?

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.

Can I suppress this rifle?

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.