Here’s what CMMG had to say:
Boonville, MO – CMMG® expands on the popular .22LR Conversion Kit with the addition of the Mk57 .22LR AR Conversion Kit. Easily convert your CMMG 5.7x28mm upper receiver group into a .22LR by swapping the bolt-carrier group, paired with the 5.7x28mm upper and any Mil-Spec AR15/Mk4 lower receiver, while using a dedicated CMMG .22LR magazine.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.The Mk57 .22LR Conversion Kit is designed to be used with all CMMG Mk57 5.7x28mm upper receiver groups and bolt/barrel combinations when paired with any Mil-Spec AR15/Mk4 lower receiver. CMMG offers Mk57 5.7x28mm complete uppers in 5-inch, 8-inch and 16-inch barrel lengths.Converting any CMMG Mk57 upper to shoot .22LR is a great way to reduce cost with each pull of the trigger, all while reducing recoil and muzzle flash. 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.Mk57 .22LR Conversion Kits come with a dedicated bolt-carrier group and the choice of one or three 25rd magazine(s) with an MSRP of $199.95 to $229.95.For States with magazine capacity restrictions, the Mk57 .22LR Conversion Kit can be purchased with 10rd magazines.