The CMMG Resolute MK4 upper group (brand part number 55BB40B-AB) is a fully assembled 5.56x45mm NATO AR-15 upper built around a 16.1-inch barrel, sold without a bolt carrier group or charging handle so you can drop in your own. Because this is a bare upper receiver assembly with no included lower, it isn’t a complete firearm on its own. Finished in matte black and cut with a 1:7 twist to stabilize a full range of 5.56 bullet weights, it’s a fast way to add a proven CMMG upper to an existing lower or start a new build. Since the BCG and charging handle aren’t included, make sure you have compatible parts on hand before your build is ready to run.

Key Specifications

• Chambered in .223 Remington/5.56x45mm NATO.
• Barrel length measures 16.1 inches.
• Rate of twist is 1:7 inches.
• Overall upper length measures approximately 31.2 inches.
• Sold as a fully assembled upper group.
• Finished in matte black.
• Ships without a bolt carrier group or charging handle.

Frequently Asked Questions

Does this upper include a bolt carrier group? No, it’s sold without a BCG or charging handle, so you’ll need to supply your own.

Is this a complete firearm? No, it’s a bare upper receiver assembly with no lower receiver included.

Buy the CMMG Resolute MK4 5.56 16.1 Inch Upper Group, No BCG or Charging Handle

Add a proven CMMG upper to your build. Order from our CMMG lineup of AR-15 uppers from a Lubbock, TX gun shop.