The sudden resurgence of the 5.7x28mm cartridge got another boost with the recent announcement by CMMG of its new 5.7 AR Conversion Magazine. The CMMG 5.7 AR Conversion Magazine holds 40 rounds of 5.7x28mm. It fits and functions within a standard mil-spec AR-15 lower. The magazine pairs with CMMG’s 5.7x28mm Radial Delayed Blowback upper receiver.

CMMG 5.7 AR Conversion Magazine

The 5.7 AR Conversion Magazine converts a mil-spec AR-15 into a 5.7x28mm. It provides easy transition from 5.56 to 5.7x28mm, while maintaining the familiar controls on the existing lower.

To convert, simply attach a CMMG 5.7x28mm Radial Delayed Blowback complete upper to an existing AR-15 lower. Then insert CMMG’s 5.7x28mm AR Conversion Magazine. That’s it. CMMG recommends using a standard carbine buffer and action spring to reliably cycle. The conversion magazine also retains last round bolt hold open.

CMMG offers a complete line of firearms in BANSHEE and RESOLUTE models designed for 5.7 magazines. Each features CMMG’s Mk4 lower receiver and a dedicated 5.7x28mm Radial Delayed Blowback upper receiver.

CMMG also offers complete 5.7x28mm upper receiver in BANSHEE and RESOLUTE models. Each comes in three different barrel lengths: 5, 8 and 16 inches. Each complete upper receiver uses CMMG’s patented Radial Delayed Blowback operating system.

Bolt and barrel kits in 5, 8 and 16-inch barrel lengths will also become available, according to CMMG. The bolt and barrel kits will work with CMMG Mk57 lower receivers, along with Mk4/AR-15 lowers (when using the CMMG 5.7 Magazine).

The 5.7 AR Conversion Magazine retails for $39.95. For more information, please visit

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