CMMG UPPR RSLT MK4 6MM ARC 16.1″ BLK

Description

The CMMG Resolute MK4 upper group in 6mm ARC is built for shooters who want to stretch the effective range of an AR-15 platform without moving to a larger frame. The 6mm ARC cartridge was developed specifically for this purpose: it offers a high ballistic coefficient relative to its case size, which translates to less wind drift and more retained velocity at distance compared to conventional intermediate rifle cartridges. That makes this upper a practical choice for precision target work and hunting applications where shots extend beyond what 5.56 NATO handles comfortably.

The 1:7.5-inch twist rate is worth understanding before you stock up on ammunition. That rate stabilizes the heavier, longer 6mm projectiles that make the cartridge useful at range — lighter or shorter bullets in this bore diameter may be over-stabilized, so handloaders and handpickers should select accordingly. The rifle-length gas system spreads the extraction impulse across a longer dwell time than a carbine-length setup would, which generally softens felt recoil and reduces bolt velocity — a meaningful advantage when you are running a precision-oriented build where shooter fatigue and split-time matter.

The barrel is 416 stainless steel with a black salt bath nitride finish, which provides corrosion resistance without adding the dimensional variability that can come from some external coating processes. Muzzle threads are cut 5/8″-24, the standard for this bore diameter, giving you a straightforward path to a variety of muzzle devices. The billet 6061-T6 aluminum upper receiver pairs with the CMMG EML15 M-LOK handguard, and the assembly ships complete with a bolt carrier group, ambidextrous charging handle, and polymer dust cover — ready to drop onto a standard AR-15 lower. The Armor Black Cerakote finish ties the assembly together visually while adding a layer of wear and corrosion protection.