CMMG Resolute MK4 Upper Group – 5.56 NATO, 16.1″ Barrel, M-LOK

Description

The CMMG Resolute MK4 upper group is the fast lane to a well-built 5.56 carbine. It comes assembled around a 16.1-inch 4140 chrome moly steel barrel with a 1:7 twist, so it stabilizes the full range of common .223 Rem and 5.56 NATO loads, from 55-grain plinkers to heavier match and defensive bullets. Since it ships without a bolt carrier group or charging handle, you get to spec those two parts yourself and keep control over your build.

What Makes the Resolute MK4 Upper Tick

The barrel runs a mid-length gas system paired with a .750 low-profile gas block, which is the sweet spot for a 16-inch 5.56. That setup softens the recoil impulse and eases wear on internals compared to a carbine-length gas port, so cycling feels smoother round after round. The muzzle wears a standard A2 flash hider on 1/2-28 threads, and if you'd rather run a brake, comp, or a suppressor down the road, swapping it out takes just a wrench and a few minutes.

Handguard and Real-World Use on the Resolute MK4

Up front sits CMMG's 15-inch EML15 M-LOK free-float handguard. It carries M-LOK slots at the 3, 6, and 9 o'clock positions plus a top section, giving you plenty of real estate for a light, laser, bipod, or hand stop without crowding the barrel. Because it free-floats, your accessories aren't putting pressure on the barrel, which helps keep groups consistent. The matte black finish on the receiver and handguard shrugs off handling and holds up to range time and weather.

This is a solid foundation for a first build or an upgrade to an existing lower. Add a quality BCG and charging handle, snug it to any mil-spec AR-15 lower, and you've got a dependable carbine ready for range days, training, or general-purpose shooting. CMMG backs its work with a lifetime quality guarantee against material and workmanship defects, which is a nice bit of peace of mind on a part you plan to shoot hard.