The CMMG Resolute Mk57 5.7x28mm rifle in Armor Black (CMMG part no. 57A230FAB) brings a fast, light-recoiling cartridge to a carbine-length AR-style rifle. CMMG designed the Mk57 platform exclusively around FN Five-seveN-style magazines without giving up AR features such as last-round bolt hold open, so the same cartridge and magazines can serve a pistol and a carbine. It runs on CMMG’s Radial Delayed Blowback system, which the maker credits with a softer recoil impulse and reduced bolt weight. The ZEROED parts suite, a RipStock buttstock and an EML15 M-LOK handguard round out a rifle for range work and recreational shooting where low recoil and short-range penetration matter.

Key Specifications

• The chambering is 5.7x28mm, a cartridge CMMG describes as fast and light with minimal recoil and good penetration at short range.
• The barrel is 16.1 inches with a 1:9 twist, a carbine length matched to the 5.7x28mm round.
• The action is Radial Delayed Blowback, which gives a softer recoil impulse and a lighter bolt than straight blowback.
• The muzzle carries a ZEROED RBB brake on a 1/2×28 thread, so the threads accept standard 1/2×28 muzzle devices.
• Feeding is from a 20-round magazine in the FN Five-seveN pattern, which keeps interchangeability with pistols that use the same magazines.
• The stock is the CMMG RipStock with a six-position fastback receiver extension for adjustable length of pull.
• The handguard is the EML15 M-LOK with slots at 3, 6, 9 and 12 o’clock, leaving room for lights and grips.

Frequently Asked Questions

Which magazines does it use? The Mk57 platform is designed exclusively to accept FN Five-seveN-style magazines, and this rifle ships with a 20-round magazine.

Does it keep AR controls? Yes. CMMG built the Mk57 to retain AR functions such as last-round bolt hold open, and it uses a ZEROED 60/90-degree ambidextrous safety and a ZEROED drop-in trigger.

What is Radial Delayed Blowback? It is CMMG’s delayed-blowback action, adapted from the .45 ACP MkG platform, that the maker says produces a softer recoil impulse and reduced bolt weight compared with traditional straight blowback.

Buy the CMMG Resolute Mk57 Rifle, 5.7x28mm, 16.1-Inch, Armor Black, Muzzle Brake, 20-Round

Order it from our Lubbock, Texas gun shop for fast, insured shipping to your FFL, and see the rest of our AR rifles for more CMMG options. The Mk57 suits shooters who want a flat, light-recoiling 5.7x28mm carbine.