CMMG is announcing a new addition to their line-up of AR-15-pattern pistols, the new Mk4 K chambered for 5.56 NATO. Unlike their 300 AAC Blackout and 9mm pistols, the 5.56 model sports a longer 12.5-inch barrel, up from 8.2, which helps boost muzzle velocities.
Cartridges like 5.56 NATO and .223 Remington lose a lot of speed if they are fired from barrels that are cut down too far. The longer barrel will have improved ballistics and a flatter flight path than a similar gun with a shorter barrel while still keeping the overall length down and maneuverability high.
It also gives the pistol an edge in the reliability department as short-barreled ARs sometimes don’t stay pressurized long enough to cycle dependably, particularly with slow-burning, low-pressure ammo. The barrel has a medium weight contour and a 1-in-7 twist.
The shorter barrel makes a big weight difference. Unloaded the pistol weighs just 5.3 pounds, which is fantastic. The overall length is 28 inches.
The Mk4 K AR pistol comes with a Magpul MOE pistol grip and stock, an A2-style flash and an ambidextrous rear sling mount end plate. Mk4 pistols ship with a 30-round Gen 2 Magpul PMAG standard.
One feature that makes the pistol really stand out is the long, free-floating handguard. The Mk4 comes with CMMG’s RKM11 rail. The handguard has KeyMod slots three-, six- and nine-o’clock positions that users to mount accessories directly to the handguard. CMMG offers separate 5-slot adapter rails for use with Picatinny accessories. The 12-o’clock rail is Picatinny along its full length for use with standard iron sights and other sights or scopes.
The Mk4 is an “optics-ready” pistol, meaning the user supplies their own sights. This of course keeps the initial price down while leaving optics options completely up to the user.
And naturally this is a prime candidate for a stabilizing arm brace. It’s almost a surprise CMMG isn’t shipping with one affixed.
The rest of the specifications are fairly boilerplate and largely MIL-SPEC, including the forged 7075-T6 hard-anodized aluminum receivers and fire control group.
CMMG has set the Mk4 K AR’s MSRP at $1,049, which is competitive. Real-world prices should be under $1,000 by a pretty good margin. All CMMG firearms come with a lifetime guarantee.