CMMG is rolling out a new pistol-caliber AR chambered for 5.7x28mm, the Mk57. The new 5.7mm guns are offered in pistol and NFA-regulated short-barreled rifle configurations and they use standard Five-seveN magazines.
The company is bringing to market one SBR and three pistols, two with 5-inch barrels and one with an 8-inch barrel. The SBR comes with a CMMG RipStock installed while the pistols have a few different options.
Depending on the model, the pistols come with a bare buffer assembly, a Gear Head Works Tailhook Mod 2 brace or Shockwave stabilizer. All are offered in 11 different Cerakote finishes. CMMG is delivering these Mk57s in an array of semi-custom colors in addition to the standard tactical trio of black, olive drab and flat dark earth.
Depending on the configuration the Mk57 weighs in at just 4.6 to 5 pounds unloaded. Recoil won’t be an issue, either. Not only is 5.7x28mm a low-recoiling cartridge, the Mk57 uses a delayed-blowback operation to reduce reciprocating mass.
“The 5.7 is an intriguing round that is perhaps best known for its relatively lightweight bullet design and impressive velocities,” said CMMG CEO Chris Reinkemeyer. “From an engineering perspective, we were excited to pair the 5.7 with our Radial Delayed Blowback system. I think it’s safe to say that this combination makes the Mk57 one of the lightest recoiling pistol caliber carbines on the market.”
The guns have ambidextrous controls including the selector, charging handle and sling plate. They also have M-Lok forends and Magpul pistol grips. The SBR comes with a Magpul foregrip as well.
Each gun comes with one standard-capacity 20-round Five-seveN mag by ProMag. CMMG offers +10-round magazine extension kits as well for $17. The kits come with an enlarged baseplate and extended magazine spring.
FN developed the 5.7x28mm cartridge for one of the first personal defense weapons to see wide success, the FN P90. FN developed the P90 as a compact alternative to rifles and carbines for security teams and vehicle crews, then produced the Five-seveN pistol to use the same cartridge.
While the PDW concept would eventually take off with compact AR-pattern rifles chambered for 5.56 NATO and 300 AAC Blackout, 5.7x28mm earned its own solid following. With its low flash signature and recoil, 5.7x28mm is here to stay.
CMMG is taking things full circle with the Mk57. By combining the PDW-optimized 5.7x28mm cartridge with AR features and handling, they’ve got a solid setup with their new series.