The CMMG Resolute Mk4 upper group in .300 Blackout (brand part no. 30B12BBAB) is a complete direct impingement upper with a 16.1-inch barrel, finished in black Cerakote. CMMG builds it on a billet 6061 T6 aluminum upper receiver and fits a CMMG ZEROED muzzle brake, an EML15 M-LOK handguard, an adjustable gas block and a ZEROED ambidextrous charging handle. The 1:7 twist barrel is made from 4140CM steel with a carbine-length gas port. It is a ready-to-run way to turn a Mk4 lower into a .300 Blackout rifle for suppressed use, hunting or range work.

Key Specifications

• The caliber is .300 BLK, CMMG’s designation for .300 Blackout.
• The barrel length is 16.1 inches, with an MT contour and a 1:7 twist.
• The barrel material is 4140CM steel, and the gas port location is carbine.
• The operating system is direct impingement, with an adjustable .750-inch gas block.
• The muzzle device is the CMMG ZEROED muzzle brake on a 5/8×24 thread.
• The upper receiver is billet 6061 T6 aluminum on the Mk4 platform.
• The handguard is the CMMG EML15 M-LOK, with slots for accessories.

Frequently Asked Questions

What is included in the upper group? CMMG lists the upper receiver, the 16.1-inch barrel, the ZEROED muzzle brake, the adjustable gas block, the EML15 M-LOK handguard and the ZEROED ambidextrous charging handle. CMMG sells a separate version without the bolt carrier group or charging handle.

What thread does the muzzle brake use? The CMMG ZEROED muzzle brake mounts on a 5/8×24 thread.

What is the barrel twist and length? The barrel is 16.1 inches long with a 1:7 twist and an MT contour.

Buy the CMMG Resolute Mk4 Upper Group, .300 Blackout, 16.1-Inch

A complete upper makes a .300 Blackout build a two-pin job. Order it from our Lubbock, Texas gun shop for fast shipping, and see more AR-15 uppers while you are here.