Originally chambered in 5.7x28mm, CMMG's Mk57 gets the conversion treatment with the company announcing a new .22 LR conversion kit for the Mk57. 

The Mk57's bolt-carrier group swaps out to a .22 LR version that marries to the Mk57's upper and and any mil-spec AR-15/Mk4 lower receiver to offer a rimfire package with the Mk57 look. The conversion kit is topped off with three CMMG branded 25-round, .22 LR magazine. For states that are bound by mag restrictions, CMMG does offer 10-round mags. 

The conversion kit ships with three .22 LR mag and bolt carrier group. (Photo: CMMG)

The company has brought conversion kits to market before, with offerings in 9mm and .22 LR. 

"CMMG prides itself on caliber flexibility. The ability to shoot multiple calibers with one lower has its obvious advantages. One firearm, reduced cost, muscle memory and storage to name a few," CMMG said in a news release.

"Converting any CMMG Mk57 upper to shoot .22 LR is a great way to reduce cost with each pull of the trigger, all while reducing recoil and muzzle flash," says CMMG. "Anyone who is interested in 5.7x28mm. but concerned about ammo prices, can take advantage of cost-effective rimfire training. It’s the ultimate tool for young or first-time shooters."

OreGear has the low-down on the MK57 Conversion in the 20~ minute video, below. 


The CMMG .22 LR Conversion Kit for the Mk57 retails for around $229.

revolver barrel loading graphic