The CMMG Banshee Mk4 Upper Group in .300 BLK (brand part no. 30B81F4AB) makes it easy to add one of the most versatile cartridges in the AR-15 world to an existing lower, or to top off a new build with one of the most compact, stylish .300 BLK upper groups on the market. .300 BLK excels from close quarters to mid-range, with loadings optimized for both subsonic/suppressed and supersonic use, giving real flexibility for a single upper. This Mk4 platform Banshee upper ships complete with a bolt carrier group and CMMG’s ZEROED accessories, including an AR15 polymer dust cover, an AR15 ambi charging handle, and a linear compensator, so there’s nothing extra to source. It runs an 8-inch, 4140CM SBN barrel with a 1:7 twist on a direct impingement operating system, a 0.750-inch non-adjustable gas block fed from the pistol gas port location, a billet 6061 T6 aluminum upper receiver, and a CMMG EML7 M-LOK handguard finished in standard Cerakote. Overall upper length runs approximately 16.5 inches and it weighs about 3 pounds. Because this upper ships without a lower receiver, it is not itself a complete firearm; an 8-inch barrel is well under the 16-inch federal minimum for a rifle-configured (shouldered) lower, so this upper group should only be installed on a registered short-barreled rifle, an NFA-compliant braced pistol build, or a pistol-configured lower to stay compliant.

Key Specifications

• Chambered in .300 BLK on the Mk4 platform.
• 8-inch barrel length with a 1:7 twist rate.
• Barrel material: 4140CM SBN, direct impingement operating system.
• Ships complete with a bolt carrier group and CMMG ZEROED accessories.
• Upper receiver: billet 6061 T6 aluminum.
• Handguard: CMMG EML7 M-LOK.
• Overall length approximately 16.5 inches, weighing about 3 pounds.
• Finished in standard Cerakote.

Frequently Asked Questions

Does this upper group include a lower receiver? No, this is an upper group only and requires a compatible AR-15 lower to complete a firearm.

Is an 8-inch barrel legal to run on any lower? Only on a registered short-barreled rifle, an NFA-compliant braced pistol build, or a pistol-configured (non-shouldered) lower; installing it on an unregistered rifle-configured lower would create an illegal short-barreled rifle.

Does this upper ship with a bolt carrier group? Yes, it ships complete with a BCG and CMMG’s ZEROED accessories, including the charging handle and linear compensator.

Buy the CMMG Banshee Mk4 8-Inch Upper Group

Order it from our Lubbock, Texas gun shop as soon as it’s available to ship, and add a compact, ready-to-run .300 BLK upper to your collection.

Shop more from CMMG and browse our full AR15 uppers selection.