CMMG 55BB40BAB Resolute MK4 | 5.56 NATO | 16.1 in

The CMMG Resolute MK4 assembled upper is a partial AR-15 upper group chambered for .223 Rem/5.56 NATO and built around a 16.1 inch barrel. It pairs a free-float M-LOK handguard with a non-adjustable gas system intended for standard rifle-length operation. This unit ships without a bolt carrier group or charging handle and is intended to complete a compatible AR-pattern lower for range or field use.

Product Specifications

• The manufacturer is CMMG.
• The model is Resolute MK4.
• The manufacturer part number is 55BB40BAB.
• The UPC is 810103473461.
• The cartridge/chambering is .223 REM/5.56 NATO.
• The barrel length is 16.1 inches.
• The rate of twist is 1:7″.
• The barrel material is STEEL.
• The handguard type is M-LOK Free-Float.
• The handguard finish is listed as Armor Black.
• The muzzle threading is 1/2-28.
• The upper is supplied as a partial upper group with no bolt carrier group and no charging handle included.
• The unit includes an A2 flash hider with 1/2-28 threads.
• The gas block is a non-adjustable .750 gas block.
• This item is categorized as an AR-15 accessory.

This assembled upper provides a practical foundation for finishing an AR-15 build where a mid-length, service-style barrel and M-LOK modularity are desired. It is suited to range training and general precision or target shooting applications when paired with an appropriate lower and components.