CMMG Resolute MK4 Upper — .300 AAC Blackout 16.1″ Barreled Upper

Description

The CMMG Resolute MK4 gives you a well-built starting point for a .300 Blackout carbine without locking you into a full rifle purchase. It comes assembled with everything above the receiver split done for you, so all that's left is dropping in your bolt carrier group, charging handle, and mating it to any standard AR-15 lower. That makes it a smart pick whether you're piecing together a fresh build or converting a spare lower into a hard-hitting .30 caliber shooter.

What Sets the Resolute MK4 Upper Apart

The heart of this upper is a 16.1-inch barrel made from 4140 chrome moly steel with a Salt Bath Nitride finish, which holds up well against wear and corrosion inside and out. It runs a 1:7 twist, which handles the full range of .300 Blackout loads nicely, from heavy subsonic rounds for suppressed shooting to lighter supersonic ammo for range work and hunting. A carbine-length gas system keeps cycling smooth, which matters a lot with a caliber that was purpose-built to run well in shorter barrels.

Handguard and Muzzle Details on the Resolute MK4

Up front you get CMMG's 15-inch EML15 aluminum handguard with M-LOK slots along the sides and bottom, plus short Picatinny sections front and rear on top for iron sights. That gives you plenty of room to mount lights, grips, bipods, and whatever else your setup calls for. The barrel is threaded 5/8"-24 and ships with a CMMG A2 flash hider, so you're ready to swap in a suppressor or another muzzle device down the road.

One of the best things about .300 Blackout is how much AR-15 hardware carries straight over. It uses standard 5.56 magazines and components, with the barrel being the main difference, so finishing this upper is about as painless as an AR build gets. Pair it with a quality .300 BLK-compatible BCG and a charging handle of your choice and you've got a versatile, suppressor-friendly carbine ready to go.