CMMG BANSHEE MK4 Upper Group 300 BLK 8" Barrel - Black

The CMMG BANSHEE MK4 upper group in 300 BLK with an 8-inch barrel is a complete, ready-to-run solution for shooters who want a compact, versatile platform that handles everything from subsonic suppressed rounds to supersonic loads. Whether you're building a short-range defensive carbine, a specialized hunting upper, or a compact range gun, this upper group ships fully assembled with bolt carrier group and all critical components already installed and zeroed—no gunsmithing required. The 8-inch barrel in 300 BLK delivers the round's sweet spot for compact form factor without sacrificing the chambering's inherent flexibility across ammunition types.

CMMG engineered the BANSHEE MK4 around the direct impingement operating system with pistol-length gas, which keeps the profile lean and reliable in a short package. The 1:7 barrel twist stabilizes both heavy subsonic and standard supersonic projectiles, making this upper at home with suppressed 220-grain rounds or full-velocity hunting ammunition. The billet 6061-T6 aluminum upper receiver is paired with a CMMG EML7 M-LOK handguard, giving you a modern platform with plenty of room for mounting lights, lasers, or other accessories without bulk. The included CMMG ZEROED linear compensator (5/8 x 24 thread) tames recoil and keeps the muzzle rise predictable, while the non-adjustable 0.750-inch gas block maintains consistent cycling.

The 300 BLK upper is built on the Mk4 platform and comes finished in Cerakote for durability and aesthetics. You'll get an ambi charging handle and polymer dust cover in the box—everything needed to mount this onto a compatible AR-15 lower receiver and get to work. At 16.5 inches overall and just 3.0 pounds, it's genuinely compact without compromise.

Key Features

• 8-inch 300 BLK barrel with 1:7 twist—stable across subsonic and supersonic loads
• Complete upper assembly: bolt carrier group, charging handle, and dust cover included and zeroed
• CMMG ZEROED linear compensator (5/8 x 24) reduces recoil and muzzle rise
• Direct impingement with pistol-length gas for compact, reliable operation
• Billet aluminum upper receiver paired with CMMG EML7 M-LOK handguard
• Non-adjustable gas block for consistent cycling without user tuning
• Cerakote finish for corrosion resistance and clean appearance
• 16.5 inches long, 3.0 pounds—true compact platform

Specifications

Frequently Asked Questions

Is this a complete upper I can mount straight to my AR-15 lower?

Yes. The BANSHEE MK4 upper comes with the bolt carrier group and all necessary components installed and zeroed. Mount it to any standard AR-15 lower receiver and you're ready to shoot.

What ammunition does the 1:7 barrel twist handle?

The 1:7 twist is optimized for both subsonic and supersonic 300 BLK rounds. It stabilizes heavy subsonic loads (typically 208–220 grains) as well as standard supersonic ammunition, giving you flexibility across the full range of 300 BLK loadings.

Will this work suppressed?

Yes. The 300 BLK caliber was developed for suppressed use, and the 8-inch barrel pairs well with both subsonic and supersonic ammunition when suppressed. The included linear compensator can be swapped for a suppressor-compatible muzzle device if desired.

What's included in the box?

The upper group comes complete with bolt carrier group, CMMG ZEROED ambi charging handle, CMMG ZEROED polymer dust cover, and CMMG ZEROED linear compensator. All components are assembled and zeroed—no additional parts needed to function on a compatible lower receiver.