CMMG’s New Mk57 Pistols and SBRs in FN 5.7x28mm

Press release:

CMMG has announced the release of a new line of AR pistols and short-barreled rifles (SBR’s) chambered in FN 5.7x28mm.  Available in 5-inch barreled BANSHEE and 8-inch barreled PSB configurations, each model in the new Mk57 GUARD line is fed from FN 5.7 pistol magazines and uses CMMG’s patent-pending Radial Delayed Blowback operating system.

“The 5.7 is an intriguing round that is perhaps best known for its relatively lightweight bullet design and impressive velocities. From an engineering perspective, we were excited to pair the 5.7 with our Radial Delayed Blowback system.  I think it’s safe to say that this combination makes the Mk57 one of the lightest recoiling pistol caliber carbines on the market,” said Chris Reinkemeyer, CEO of CMMG.

At the heart of the Mk57 is CMMG’s Radial Delayed Blowback operating system designed to minimize felt recoil.  It features rotating bolt that requires the recoil impulse of a round being fired in order to unlock. As each round is fired, a portion of the rearward force is exhausted in unlocking this bolt prior to driving the carrier rearward and cycling the action.  With less rearward force to compensate for, CMMG is able to use a lighter carrier and buffer than a standard blowback design would allow, thus reducing the overall reciprocating mass.

CMMG will also offer a separate lightweight buffer for use with subsonic ammunition. To overcome the reduced backpressure with subsonic loads, the lightweight buffer can help ensure that the bolt locks back after firing the last round.

The FN 5.7×28 was designed and introduced by FN Herstal with the intention of replacing the 9mm for military and law enforcement usage. While the caliber has been adopted by several agencies throughout the world, its real success came with its entry into the civilian market in the early 2000’s.

The BANSHEE in 5.7×28 has a 5-inch barrel and comes as either an SBR or an AR pistol.  The SBR version is sold with Magpul Moe vertical foregrip and features CMMG’s new RipStock.  The Ripstock allows users to quickly deploy the stock to an extended position without having to actuate a release lever.  It also has five set-screw positions that allow users to customize the length of extension to the best fit.  The AR pistol versions come with a Gear Head Works Tailhook Mod2 brace that allows users to easily extend/collapse the brace with the press of a button.

Distinguishing features of the BANSHEE also include the addition of CMMG’s new ambidextrous charging handle and RML4 M-LOK hand guard. A CMMG Premier Cerakote finish (11 different colors to choose from) is included standard with each BANSHEE. It ships with one 20-round ProMag magazine and is compatible with FN Five-SeveN pistol magazines.

Mk57 BANSHEE 5.7x28mm SBR

BARREL: 5″ MT 4140CM SBN, 1:9 Twist
MUZZLE: Thread Protector, Threaded ½-28
BCG WEIGHT: 9.9 oz.
FURNITURE: Magpul MOE Pistol Grip, Compact Receiver Extension, CMMG RipStock, Magpul MVG Foregrip, Fully Ambidextrous Sling Plate, Selector,  and Charging Handle
RECEIVERS: Billet 7075-T6 AL Lower, Forged 7075-T6 AL Upper
TRIGGER: CMMG Single Stage Mil-Spec
MAGAZINE: 20-round ProMag
WEIGHT: 4.6 lbs (Unloaded)
MSRP: $1,549.95

Mk57 BANSHEE 5.7x28mm Pistol

BARREL: 5″ MT 4140CM SBN, 1:9 Twist
MUZZLE: Thread Protector, Threaded ½-28
BCG WEIGHT: 9.9 oz.
FURNITURE: Magpul MOE Pistol Grip, Gear Head Works Tailhook Mod 2 Brace, Fully Ambidextrous Sling Plate, Selector, and Charging Handle
RECEIVERS: Billet 7075-T6 AL Lower, Forged 7075-T6 AL Upper
TRIGGER: CMMG Single Stage Mil-Spec
MAGAZINE: 20-round ProMag
WEIGHT: 4.7  lbs (Unloaded)
MSRP: $1,549.95

Mk57 5.7x28mm PSB

The Mk57 PSB Pistol includes an 8-inch barrel and a KAK Shockwave Brace.  It also sports a CMMG RML7 M-LOK hand guard and CMMG A2 Compensator.  It ships with one 20-round ProMag magazine and is compatible with FN Five-SeveN pistol magazines.

Mk57 PSB 5.7x28mm Pistol
BARREL: 8″ MT 4140CM SBN, 1:9 Twist
MUZZLE: CMMG A2 Compensator, Threaded ½-28
BCG WEIGHT: 9.9 oz.
FURNITURE: Magpul MOE Pistol Grip, KAK Shockwave Stabilizer and Brace
RECEIVERS: Billet 7075-T6 AL Lower, Forged 7075-T6 AL Upper
TRIGGER: CMMG Single Stage Mil-Spec
MAGAZINE: 20-round ProMag
WEIGHT: 5 lbs (Unloaded)
MSRP: $1,399.95

Mk57 5.7x28mm Pistol

The Mk57 Pistol includes an 8-inch barrel and sports a CMMG RML7 M-LOK hand guard and CMMG A2 Compensator.  It ships with one 20-round ProMag magazine and is compatible with FN Five-SeveN pistol magazines.

Mk57 PSB 5.7x28mm Pistol
BARREL: 8″ MT 4140CM SBN, 1:9 Twist
MUZZLE: CMMG A2 Compensator, Threaded ½-28
BCG WEIGHT: 9.9 oz.
FURNITURE: Magpul MOE Pistol Grip
RECEIVERS: Billet 7075-T6 AL Lower, Forged 7075-T6 AL Upper
TRIGGER: CMMG Single Stage Mil-Spec
MAGAZINE: 20-round ProMag
WEIGHT: 5 lbs (Unloaded)
MSRP: $1,349.95

CMMG RipStock

Included on each BANSHEE SBR, CMMG’s RipStock is a revolutionary, retractable buttstock engineered for lightning-fast deployment to your personal setting. With Fastback Technology, simply pull straight back to extend the stock. No locking tabs to bind. P3 Technology (Personal Position Preset) allows users to adjust the indexing screw and to set your own preset.  MSRP is $199.95.

CMMG Ambidextrous Charging Handle

CMMG’s new ambidextrous charging handle is included on each model of BANSHEE and is designed to improve the operation of your AR. Gross motor skill operation, gloved operation, or just trying to get ahold of your latch with an optic mounted are greatly improved by our larger latch design. The ambidextrous latch allows for easy operation no matter which hand you use to charge the weapon. Sizes available for your AR15, AR10, Mk47 and MkW platforms. Made of 7075 Aluminum and backed by our CMMG Lifetime Quality Guarantee. MSRP’s range from $79.95 to $99.95.


  1. avatar Trollolol says:

    Magazine – 20 Round promag – ewwwww gross

    1. avatar Sich says:

      Can be used with FN FiveSeven 30-round Pistol Magazines! And CMMG also has a 10-round extension to FiveSeven 30’s “Old Style” Magazines to 40-round magazines…

  2. avatar SeamusOconnor says:

    Imagine thinking 5.7×28 is an effective round for self defense.

    1. avatar Texheim says:

      Hey, worked fine for SG1

      1. avatar Zhang says:

        Worked for LLENN too.

        1. avatar Curt in ID says:


    2. avatar Leighton Cavendish says:

      Defeats most body armor…unless it has plates.
      Lots of rounds.Easy to control.
      Pretty expensive ammo, though.
      And the weapons are not cheap, either.

      1. avatar Johnnyreb says:

        I saw a video on that some time ago on youtube. Shot from a pistol, the 5.7 could not penetrate body armor. But shot from the longer barrel of the P-90? carbine it could. (The weapon used on the Stargate series) So how long is that barrel and is it long enough to give it enough FPS to go through body armor?

        1. avatar Buffman-RANGE says:

          5.7 depending on ammo type will most certainly destroy most level IIIA panels from the Pistol..

    3. avatar jwtaylor says:

      I can tell you first hand that the SS197SR round does a number on pigs under 50 yards. I imagine it would be equally effective on humans.

      1. avatar big daddy says:

        I never saw a pig 50 yards, that would be a monster pig the size of a dinosaur.

    4. avatar Jay Wolf says:

      Here is a playlist of 3rd party testing of Elite Ammunition’s 5.7.

    5. avatar Red in CO says:

      Uhh… it’s not a bad option, actually. With proper shot placement and follow up shots, it can be effective. Ballistically similar to a .22 mag, which while not massively powerful can certainly do some damage. Biggest advantage I could see with this rifle is that the 5.7 has similar characteristics with regard to overpenetration as the 5.56, but you can get that out of a much shorter barrel. In other words, if you live in a condo or an apartment building with neighbors on both sides, above, and below you, this could make for a phenomenal choice

  3. avatar Hasaf says:

    I can see this as an interesting choice for people looking for a barrier sensitive Home Defense platform. While most of the firearm community interest is in barrier blind loading, for people in urban environments, barrier sensitive loading’s make more sense.

    1. avatar Chicago steve says:

      I’m sorry but chambering anything in something else besides 6.5 Creedmoor is so not hot right now.

  4. avatar Oldsarge says:

    I’ve always enjoyed my FiveseveN. May need to grab one of these carbine SBRs. For the price though, may as well get a PS90 and get it converted to SBR.

    1. avatar M1Lou says:

      This was exactly my thought. I got the MIL/LE deal on my PS90 and paid $950 for mine. I’ve seen them around $1000-1300 regular price. 50 round mags are usually under $20 for FN when I bought mine and if you want to chance it, grab some Korean mags for less than that and hope they work right. I plan to SBR mine and slap a can on it. It’s a fun little rifle.

  5. avatar ‘liljoe says:

    I’ve got a short barrel 5.7 upper on an AR pistol, makes for a great HD gun and it does have a 50 round mag so load on Sunday shoot all week :)… seems they aren’t making that upper any more though, wonder why?

    For those who poo poo this round, it’s what that terrorist used in Texas during his “workplace violence” moment. I think it will work fine for home defense.

    1. avatar Aaron M. Walker says:

      I think YOUR wrong. If my memory serves me correctly. There was an interview with surviving US soldiers of THAT terrorist tragedy. That some of our guys were shot with the FN Five7 and it fortunately failed to stop them…But of course, as anyone would know…The .357 magnum the terrorist was using turned out to be the most effective as I understand this incident…

      1. avatar ‘liljoe says:

        I know Wikipedia is a horrible source, but they say he never used the 357 magnum. I remember the reports at the time saying he used the 5.7 as well… what’s your source?

    2. avatar BillC says:

      Dude, it doesn’t matter what gun or caliber the Texas military terrorist would have had. He was straight executing unarmed dudes in the dome at point blank range at sick call. Then when he went into the actual gun fight with the MP chick, both fully expended rounds until slide-lock with neither party dead. Yeah, the real hero of the day was the FiveseveN. Suuuureee.

      1. avatar 'liljoe says:

        Shifting goalposts… my post was responding to those saying it’s a crap round. Whether you shoot at an unarmed assailant or an armed one (does that automatically give him 5+ armor and 5+ health when he is armed?), my point was that it has been used in recent history with terminal results.

        The response was that he didn’t use that round to kill anyone, to which I responded.

        You then shifted the point of the discussion to suit your needs, maturely too! Congratulations, you win the internet for today!

  6. avatar Gov. William J Le Petomane says:

    Hmmm… $1400 for a 5 pound pistol that shoots a round almost as powerful as 9 mm. Let’s go with ‘pass’ on this one.

    1. avatar Sich says:

      Maximum Range of 9×19 Pistol ~250-meters vs. Maximum Range of 5.7×28 Pistol ~1,510-meters. Hummm, ~6.04 times it range! No Brainer…

      1. avatar million says:

        1500 meters? according to this ballistics chart, a 30gr bullet goes 250m from a 16″ barrel, then tumbles into the dirt.

        1. avatar Binder says:

          Sich But honestly you know NOTHING about firearms nor ballistics. Lighter than .223 and slower, but twice the range? Read your own link, EFFECTIVE range 55 yards!!!

          Go out a shoot once in a while, you may get a better idea when something is BS

        2. avatar Sich says:

          @ Binder

          Read my comment from above! I never mentioned “Effective Range”, but “Maximum Range” instead…

        3. avatar Mike H in WA says:

          Maximum effective range is 55 yards… out of a Five-seveN, which only has a 4.8″ barrel. Out of an 8″+ barrel, I’m betting the ballistics might improve a little bit (just like a 5.56mm/.223)

      2. avatar Gov. William J Le Petomane says:

        Still that pales in comparison to the Creedmoor’s maximum range of 1500 miles.

        1. avatar Sich says:

          I was wonder when you were going to Redirect the Subject to the 6.5 Creedmoor. Which has absolutely nothing to do with the Article! Not long at all…

        2. avatar Gov. William J Le Petomane says:

          I almost said .308 instead, but we all know that the Creedmoor is the most deserving round for ridiculously over the top accolades. Like saying the 5.7’s maximum range is over 1500 yards.

        3. avatar Sich says:

          @ Gov. Willian J LePetomane.

          Maybe you should Check Out the .17 “Incinerator” in .50BMG instead.

          ( ) …

  7. avatar Alex Waits says:

    Pretty cool.

    The AR continues to be a “Wundergonne”

    Looking forward to the review.

    1. avatar barnbwt says:

      Yup, the wonder is gone…

  8. avatar Jack Moore says:

    Can’t help but notice the price is roughly the same as a PS90 so that seems like the fair comparison. I recently got a chance to shoot a P90 and I LOVED it, but there is something to be said for normal magazines and AR-15 manual of arms.

    1. avatar Binder says:

      And there is something to be said for 5.56.

      1. avatar barnbwt says:

        That it’s stupidly loud from a short barrel, have greater recoil, no better suppressed, huge powder flash that probably even makes it out of the can on a barrel this short, has a larger magazine…

        But point taken, if you’re gonna bother with a platform as large as the AR15, you might as well go with 5.56 (or at the very least nearly double your ammo capacity using an AR57 upper w/ 50 rnd P90 mag)

        1. avatar Red in CO says:

          And also that 5.56 is a joke out of a really short barrel

  9. avatar CHS says:

    The real magic here is the radial-delayed blowback system.

    One of the issues that plagues the P90/5.7×28 platform is the host guns are direct blowback. Because of that, and the tendency for dirty direct-blowback guns to blow up when using bottle-necked cartridges, the ammo can’t really be reloaded as it has a proprietary dry-lube finish applied to the cartridge case.

    However, if you have a host platform with a locked-breech delayed system, then you should be able to reload 5.7 and even hot-rod it a bit without worrying about blowing up your guns.

    This is actually pretty exciting to me.

    1. avatar barnbwt says:

      Less exciting than you’d think, sadly;
      1) The round uses so little, of such a fast burning powder, there is very little fouling blowback or otherwise
      2) The lube/film stuff lasts a few sizings, at least longer than the real limiting factor for reloading which is…
      3) The primer pockets, which even at normal 50,000psi levels, loosen up after as few as two firings

      Guys have done DI ar15 and even single shot bolt/break action builds, and the case head itself simply isn’t strong enough to go much hotter. Especially not if you have any dreams of reloading. That skinny case head simply doesn’t reinforce the (relatively) giant primer pocket well enough to reach up into magnum-rifle 60,000psi territory.

      22 Spitfire was a great alternative that probably could stand some hot-rodding without falling apart, and without giving up terribly much on the capacity (like 10% or so). But 5.7 is here to stay and is good enough at its job of approximating close-range 9mm effect but using far less to achieve that.

  10. avatar Rokurota says:

    Shouldering the brace! What’s the new new new current ATF ruling on that? I’ve lost track.

    1. avatar what would spock say says:

      It is kosher again. for the moment anyway.

  11. avatar tsbhoa.p.jr says:

    that is a hot round. i would prefer 10mm especially in cm.
    delayed roller is just way too cool. can i mention certain circa ’52 pistols yet? i don’t want to queer anyone’s deal, but pull the trigger already. if you don’t get the armorers kit there is still a healthy aftermarket for springs, firing pins and rollers. not to mention a slide release.
    sidestepping that, but still referencing 7.62×25 i gotta say: ppsh41 quest continues.

    1. avatar jwtaylor says:

      Anything in 7.62×25 gets me all tingly.

      1. avatar Mike says:

        Me too, How about an AR pistol in 7.62×25

  12. avatar David says:


    Keltec already has the market cornered with their .22 magnum pistol and carbine.

    1. avatar Jon in CO says:

      If any of their stuff actually worked, wasn’t totally put together with shit, and glued in barrels, maybe they could.

  13. avatar Mike H in WA says:

    I always thought one of the things that hurt the 5.7mm round was the lack of carbine/rifle options that took the pistol mags. What few options I saw were always the PS-90 mags. Being able to use the same mags for both your rifle and pistol always seemed like a no brainer to me. Not as powerful as 5.56mm, sure… but for a lot of applications, it’s powerful enough out of a 10″ or 16″ barrel, and without the muzzle flash/noise you’d get from an unsuppressed 5.56mm carbine or SBR.

  14. avatar Jon in CO says:

    The price on 5.7 ammo would be better if more people would buy the guns and demand more ammo. Essentially, there are the two FN guns, a couple AR57’s, and now these. There’s not a huge market for the ammo, so it’s costs a bit more.

    1. avatar Mike says:

      More ammo would be nice, Sellier & Bellot/ Magtech have been talking about making some for the last two years

  15. avatar Owen says:

    One word: LOUD

    I’ve been near a 5.7 at an indoor range. I would not want to fire one indoors. You or you loved one could loose hearing. Of course always keep ear pro by your home defense weapon.

    1. avatar M1Lou says:

      Buy a can, if you can!

  16. avatar NoNamesOnTheNet says:

    Everyone keeps talking a price and availability, but my primary carbine has been a PS90 for almost three years. It’s been a trunk gun, a bed side gun, and my get home gun, and I’ve never had an issue getting ammo.

    Few cents more than 5.56, but overall pretty comparable, especially online. Even for Green Tip SS198.

  17. avatar Nate says:

    The 5.7 cartridge gets its performance from its velocity.
    The fn rounds sold to the public do not perform to the rounds potential. Try some of elite ammunitions TB6 rounds and you’ll see what the hype is about. 2400fps out of a pistol..

  18. avatar raptor jesus says:

    About as effective as a 9mm at three times the price per round (source:

    Where do I not sign up?

Write a Comment

Your email address will not be published. Required fields are marked *

button to share on facebook
button to tweet
button to share via email