Cmmg Ar Mk 57 Conversion Kit 22Lr W/ 3 25-Rd Mags

The CMMG AR Mk57 Conversion Kit transforms your 5.7x28mm upper receiver into a practical .22 LR shooter—perfect for high-volume range days, training, or just enjoying cheap, easy-to-find ammunition. If you own a Mk57 upper and want a no-fuss way to swap calibers without breaking the bank, this drop-in conversion kit delivers exactly that: simple mechanics, minimal hassle, and a way to get trigger time without the sting in your wallet.

The conversion works by replacing your existing bolt-carrier group with CMMG's purpose-built .22 LR unit. Once swapped, your Mk57 upper mounts directly onto any mil-spec AR-15 lower receiver—no special adapters, no guesswork. The whole job takes minutes and requires zero tools, making it an ideal solution if you already have an AR platform lower on hand. Whether you're running a rifle you already own or building from scratch, this kit integrates seamlessly into standard AR-15 receivers.

The kit ships with three 25-round magazines designed to work across both mil-spec AR-15 and Mk4 magazine wells, giving you 75 rounds of capacity out of the box. That's plenty of rounds to establish a rhythm at the range or enjoy an extended plinking session. .22 LR ammunition is widely available and inexpensive, making follow-up shooting sessions budget-friendly—a real advantage when you're logging volume downrange.

Key Features

• Drop-in bolt-carrier group conversion from 5.7x28mm to .22 LR
• No tools required to swap calibers
• Compatible with any mil-spec AR-15 lower receiver
• Includes three 25-round conversion magazines
• Magazines fit both mil-spec AR-15 and Mk4 magazine wells
• Enables inexpensive, high-volume range shooting

Specifications

Frequently Asked Questions

Will this conversion kit work with my standard AR-15 lower?

Yes. Once you install the conversion kit into your Mk57 upper receiver, the upper mounts onto any mil-spec AR-15 lower receiver without modification.

Do I need special tools to install the conversion kit?

No. The conversion is a drop-in replacement—simply remove your existing bolt-carrier group and replace it with the .22 LR unit. No tools are required.

What magazines come with the kit?

The kit includes three 25-round .22 LR conversion magazines designed for both mil-spec AR-15 and Mk4 magazine wells.

Can I use standard .22 LR magazines from other rifles?

The kit is designed to use the included CMMG conversion magazines. Always verify compatibility with the specific magazines you plan to use.