CMMG Doubles Down on 5.7x28mm – 5.7 AR Conversion Magazine

CMMG 5.7 AR Conversion Magazine
CMMG 5.7 AR Conversion Magazine

U.S.A.-( CMMG Inc. has taken 5.7x28mm to a whole new level with the release of the 5.7 AR Conversion Magazine. This innovative new magazine holds 40 rounds of 5.7x28mm and is designed to fit and function in a mil-spec AR15 lower receiver when paired with CMMG’s 5.7x28mm Radial Delayed Blowback upper receiver.

The appeal of 5.7x28mm is that it is a small caliber with high velocity designed for a handgun and personal defense weapon (PDW). The cartridge was developed in response to NATO’s request for a replacement for the 9x19mm cartridge.

The 5.7 AR Conversion Magazine is ideal for anyone who has a mil-spec AR15 lower and wants to shoot 5.7x28mm. The 5.7 AR Conversion Magazine provides easy transition from 5.56mm to shooting 5.7x28mm while maintaining familiar controls on existing AR15 lower receivers.

CMMG 5.7 AR Conversion Magazine
CMMG 5.7 AR Conversion Magazine

The process of converting an AR15 to shoot 5.7x28mm is simple and quick. First, attach a CMMG 5.7x28mm Radial Delayed Blowback complete upper receiver to an existing AR15 lower. Second, insert CMMG’s 5.7x28mm AR Conversion Magazine to safely feed 5.7x28mm ammunition. CMMG recommends using a standard carbine buffer and action spring to reliably cycle the action in this configuration. The 5.7 AR Conversion Magazine also retains last round bolt hold-open functionality, allowing for faster reloads.

One the greatest benefits of using the 5.7 AR Conversion Magazine is that it allows shooters to enjoy the advantages of CMMG’s patented Radial Delayed Blowback operating system, without the need for a proprietary lower receiver. Radial Delayed Blowback has quickly become the gold standard for pistol caliber carbines, primarily due to the reduction in felt recoil versus direct blowback designs.

CMMG offers a complete line of firearms in BANSHEE and RESOLUTE models that are designed for 5.7 AR Conversion Magazines. Each is built with CMMG’s Mk4 lower receiver and a dedicated 5.7x28mm Radial Delayed Blowback upper receiver and ship with one 5.7 AR Conversion Magazine.

CMMG 5.7 AR Conversion Magazine
CMMG 5.7 AR Conversion Magazine

CMMG also offers complete 5.7x28mm upper receivers in BANSHEE and RESOLUTE models that are made with three different barrel lengths: 5, 8 and 16-inch. Each complete upper receiver uses CMMG’s patented Radial Delayed Blowback operating system and is compatible with 5.7 AR Conversion Magazines.

For gun builders, CMMG will also offer 5.7x28mm bolt and barrel kits in 5, 8 and 16-inch barrel lengths. The bolt and barrel kits will be compatible with CMMG Mk57 lower receivers, as well as Mk4/AR15 lower receivers (when used with CMMG 5.7 AR Conversion Magazines).

CMMG’s 5.7 AR Conversion Magazine will be sold both as a single unit and in packs of three to reliably feed and shoot 5.7x28mm ammunition. The MSRP for the 5.7 AR Conversion Magazine is $39.95 and for the three-pack is $99.95.

The MSRP for the 5.7 AR Conversion Magazine is $39.95 and for the three-pack is $99.95.
The MSRP for the 5.7 AR Conversion Magazine is $39.95 and for the three-pack is $99.95.

CMMG is taking pre-orders now and expects to ship by mid-February.

CMMG Lifetime Quality Guarantee

CMMG, Inc. will guarantee its products against defects in material or workmanship. CMMG, Inc. will repair, replace or substitute part(s) (at CMMG, Inc. discretion) at no charge to the customer if a defect of material or workmanship is found. All service work must be carried out by CMMG, Inc.

About CMMG:CMMG logo

CMMG began in central Missouri in 2002 and quickly developed into a full-time business because of its group of knowledgeable and passionate firearms enthusiasts committed to quality and service. Its reputation was built on attention to detail, cutting edge innovation and the superior craftsmanship that comes from sourcing all their own parts. By offering high quality AR rifles, parts and accessories, CMMG’s commitment to top-quality products and professional service is as deep today as it was when it began.

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These magazines have a flaw. The fed lips deform with heat and pressure of being loaded. After keeping several magazines loaded (for a few weeks) in a backpack (left in my vehicle during the day) i heard a buzzing noise. The magazines unload themselves. I cannot even load them to full capacity now without full cartridges “popping out” in mass. The conversion itself is awesome and everything you could want however, either buy their complete firearm that take FN mags or wait until they correct the magazine issue.


But the military adopted a Sig Sauer 9mm pistol as new issue. So, is this 5.7 now just looking for a way to pay for all the research they did. ?

Dima Prok

Why don’t they make one in 221 fireball. I would pay someone to do it. A shorter cartridge than 223 can be formed from 223 brass. Same case head, same bolt, same gas system, same bullets (lighter prefered). Using faster burning powders only 12-14gr needed which is half of typical 223 powder and it’s much more potent with velocity than 5.7 with top velocity 3582fps (reloading book data) while 5.7 factory rounds from P90 avg 2050fps with 40gr bullet and can easily use standard dirt cheap 55gr bullets as well that I personally chronographed around 3000 fps this was from… Read more »


I’m certainly a fan of personal choices – but have got to ask WHY?
Guess 5.7×28 would be a bit lighter and have slightly less recoil – but standard AR15 is already light with low recoil. While I’d like a pistol caliber AR (9mm) – my reasons would be ammo which is marginally more available at a considerably lower cost, plus usable on pistol ranges or PCC competition where 223/556 are not allowed. While 5.7 has second part – it’s a total fail on ammo cost and availability front.


I’m with you on the high cost of the ammo, but there’s one key aspect to the 5.7 that you’re not including: the fact that it can breach type 3 body armor. Considering the times in which we live, politically speaking, and societally, think mobs of mindless anarchists dressed all in black, the 5.7 PCC Would clearly meet the need to breach class 3. It would all come in a nice, neat package. However, because of cmmg’s high price tags for all of its components, I would much rather just save up and buy a P90, which comes in magazine… Read more »