SIG MPX Submachine Gun 9mm NATO, .357SIG and .40 S&W

SIG has just published a new video of their upcoming SIG MPX Submachine Gun. The MPX is notable because it fires from a closed locked rotating bolt and is gas operated, much like a rifle. Pistol caliber submachine guns usually are conventional blowback or delayed blowback because they do not generate enough gas to use a rifle-style gas system.

The SIG MPX is the world’s first submachine gun that operates with a fully closed and locked rotating bolt system, greatly enhancing operator safety.

The SIG MPX employs the SIG SAUER® battle-proven gas-operated short stroke piston system for unequalled reliability in the field, even under the most adverse conditions.

The SIG MPX is the only submachine gun that allows the operator to change barrel length, caliber and stock configuration in the field to meet mission requirements.

Easily convertible to 9mm NATO, .357SIG or .40S&W

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Brandon

    A 9.5 inch muzzle brake for the civilian version? That is ridiculous.
    Seems like they’re hoping for law enforcement sales. I wish them luck competing against HK and AR based weapons.

    By the way Steve, I posted a comment weeks ago asking you ‘not to change TFB too much’ (it got a lot of thumbs up). I think you changed too much. I really dislike the layout, and the small number of comments on recent posts makes me feel I’m not alone. The old layout wasn’t broken. And it gave this blog a distinct feel.

    • Esh325

      They did it so it’s civilian legal I suppose. I’m not crazy about it either man, but I’m sure we’ll get use to it after a while. The blog looks more professional now.

    • Brandon the small number of post is because the comments have only been available for a few hours.
      We realize some will not like the layout but we believe many will and honestly it was time for a change like this. Also we just about reached the limit of that format to handle the growth.

      • pandemicsyn

        I usually just follow the blog via google reader but the new layout is great (and Disqus rocks)

      • Kosme

        The new layout is nice, the only thing I lreally dislike is the new vote up/vote down arrows.

        • MattInTheCouv

          i’m in 100% agreement. the old thumbs were better.

    • if its gonna have 9.5″ of perm brake on it, id rather have it be another 9.5″ of real barrel

      • Observer

        With the piston system and overall weapon design, they may not have
        been able to get it working correctly with a much longer real barrel
        without significant alterations.

      • Drebin

        The 9.5″ brake also functions as suppressor baffles. You can buy it and shoot it while waiting on your tax stamp for the outer tube to slide over the brake then the end cap screws on now you have an integrally suppressed PCC. Cool idea IMO.

    • DW

      That “brake” looks more like the baffles in a suppressor…

  • Esh325

    It seems like they made it gas operated just to be different. I don’t think I’ve heard of safety issues with blowback smg’s.
    It’s possible the recoil could be less because it’s gas operated opposed
    to blowback, but we are talking about only a pistol caliber here, they
    don’t have much recoil as it is.

    • Nmate

      There are safety issues with blowback SMGs, or at least there can be. A hard jolt can send the bolt forward and fire a cartridge if it is allowed to. Most later pure blowback designs had systems to prevent this. I would say that delayed blowback is probably the best system for SMGs.

      • Esh325

        I suppose. H&K has pretty much abandoned roller delayed blowback, even the UMP is simple blowback.

        • Anonymoose

          And the MP7 uses an short-stroke piston derived from the G36…

    • Cymond

      I don’t think it’s a safety issue. A lot of people say that a gas-operated 5.56 AR carbine is softer/smoother shooting than a blowback 9mm AR carbine. I’ve seen several reviews of 9mm carbines in which people were surprised by the recoil. People say “it’s just a 9mm” but the heavy unlocked bolt slapping around makes recoil feel rough. People complain about the extra reciprocating mass in a piston-driven AR, and those are a lot lighter than a 9mm bolt. The MPX looks very smooth shooting in one of Sig’s recent video ads.

  • Dale

    While I think that this could be a big hit with police forces because of the option to have one platform for many calibers, I’m a bit skeptical about the advantages over a piston SBR in a rifle caliber. With all the 5.56 bullet weight/type options there are on the market, the only thing that I see this platform selling that hasn’t really already been done on a wide scale is the .357 SIG option, which, in my opinion, is nothing short of awesome. I’m just wondering whether or not departments/agencies will bite for this platform due to commonality with the AR platform or because their HK subguns are aging. I’m hoping that this new platform does well.

  • Hawk

    Seriously, no .45 ACP version of this for an LE market? If anybody was seriously gonna adopt this over an SBR in the first place, they ruined their chances when they didn’t include the tried and trusted person-stopper.

    • They could always use the KRISS?

    • Because 9mm and .40 just don’t ever stop people. Right.

    • Dual Sport

      I would like a 45 ACP version but not b/c its so much better than 9 or 40. That is simply a cartridge I like a lot and seems to be overlooked most often in an SMG style firearm. I guess we also have to consider a European company making something overseas will think first of cartridges popular in Europe and go from there.

  • USa

    any word on a price? prob $2000+

    • Dual Sport

      Unfortunately with current gun industry pricing you could be right. I saw a Sig 7.62 AR which retails for less than $2,000.00 on a table for over $3,000.00 last weekend. This SMG in an easily SBR’ed package would be a big seller but would need to be less than $1,500.00 at the maximum to really take off. The 9mm chambering is nice b/c of once cheap ammo but those days could be numbered, or over depending on who you listen to.

    • Dual Sport

      I forgot to mention the possibility that Sig may not even bring this to market until political winds have settled down so Sig can see which way the winds are blowing. Gearing up to manufacture a new firearm only makes since if you can produce it and recoup the investment by selling in quantity.

  • ChrisM

    I’d be cashing out the kid’s college fund right now……….if I could get one with a giggle switch. But since I’m not worthy……..meh.

  • ¤

    I would have preferred a longer barrel to an dumb looking muzzle break… oh well it will probably cost 1k+ and be way over what I would pay for a semi auto Pistol caliber carbine anyways, looks nice though.

    • Burkefett

      As has been stated several times, that ‘dumb looking muzzle brake’ is a set of permanently attached suppressor baffles, lacking only an outer sleeve and a tax stamp to become integrally suppressed.

  • Llewellyn

    What the heck is NATO mud? was it designed to combat the formidable Warsaw pact mud?

    • noob

      NATO mud is more accurate and more modular than its more rugged soviet counterpart.

    • TCBA_Joe

      NATO mud is a series of specific recipies and proceedures in order to standardizing testing for military organizations within NATO.

  • John

    Looks like a MP5

  • John

    Reminds me of the KAC PDW also

    • Juice

      Too bad the KAC PDW gets more attention for Airsoft then it does for live-fire versions, i can barely find a good video on it…

  • PoBoy

    Isn’t that some shit? Nice piece of kit.

  • DougE

    If “NATO mud” is what our defense industry has turned to, sequestration NEEDS to happen.

    • TCBA_Joe

      Read above, NATO mud is s just the standards laid out by NATO to standardize mud testing and keep a certain standard. Might shock you there’s all kinds of NATO standardized testing

  • Bob Z Moose

    A sub gun? In 357 SIG?! I WANT CIVI VERSION!!!

  • Brian in Seattle

    About time there was a sub-gun in 357 SIG from SIG. Kind of an updated 7.62×25. I’d be interested in what sort of muzzle velocity this gun is getting. And why no 10mm?

    • Anonymoose

      “Long-action” and “short-action” exist in the pistol-caliber world as well. Glocks (17/22/31/37 vs. 20/21) and MP5s are a prime example of this, but the HK UMP can change from short (9×19, .40) to long (.45) because it was designed specifically to do so. If they were going to make a “long-action” MPX I’d like to see it come in 10mm and .45 and someone make 9×25 and .460 conversions for it, but 10 is a rare caliber with government worldwide these days unfortunately, and only the US still uses .45 in any official capacity.

      • Brian in Seattle

        Didn’t the FBI have HK MP5 in 10mm?

        • Anonymoose

          Yeah, back in the late-80s/early-90s they made a 10mm MP5 called the MP5/10. Tom Clancy erroneously referred to it in several of his novels as the “MP10” (irl the MP10 is an American clone of the MP5N with a redesigned upper receiver w/Picatinny rails and new sights, monolithic taclight-forend, and a folding stock based on the UMP’s). Regular 9×19 MP5s can’t be converted to MP5/10s or MP5/40s due to the receiver being modified and stuff for the new cartridges. MP5/10s and MP5/40s also use straight, translucent plastic mags iirc. They discontinued the MP5/10 and MP5/40 when they introduced the UMP (which was originally introduced in .40S&W, just like the USP).

  • Bull

    “Pistol caliber submachine guns usually are conventional blowback or
    delayed blowback because they do not generate enough gas to use a
    rifle-style gas system”

    not true at all. its just a bit more difficult to design the system and i guess more expensive to manufacture. and the pros arent as big as in a rifle. a straight blowback bolt in 5.56 should weight around 3 kgs after all!

    “The SIG MPX is the world’s first submachine gun that operates with a
    fully closed and locked rotating bolt system, greatly enhancing operator
    safety” ive seen gas op pistol caliber rifles /subguns before. although they where one offs.

    “The SIG MPX is the only submachine gun that allows the operator to
    change barrel length, caliber and stock configuration in the field to
    meet mission requirements.” you could do this with a UZI too.

    i like it though. but they should add a few more calibers. like .45 , .460 rowland and why not .50 AE? powerful handgun calibers are great for these types of weapons after all. and since its gas op it well suited for them 🙂

    • Anonymoose

      I would love a .460 Rowland SMG/carbine, or even a .45 Super one, however .50AE offers no tactical advantage over the three main calibers (9mm, 10mm, and 11.43mm) other than FIDDY-KIL DEAGLE BRAND DEAGLE XDXDXD!!!!11

  • kivaari

    AR-15 and MP5 got drunk and went to bed, nice gun though

    • Anonymoose

      It’s based on the SIG516 I think.

    • Juice

      I think they made intense eye-contact with a UMP45/9 while doing the deed.

      • noob

        Gun porn. See the mag slide into the feed lips, the cycling of the action. The eruption of metal laced flame…

  • Mike Knox

    Finally, an automatic in .357 SIG..

  • This gun in .357 SIG can be great PDW.

    By the way, since the .357 SIG and the .40 has the case dimensions, could one gun being able to shoot both calibers with just a barrel swap? That seems quite cool.

  • brian

    I’m gonna have to call out sig on the “first rotating and locked bolt system” I remember that the chinese had a subgun that had some ak internals. here’s the link
    (of course I may be wrong somewhere)

  • Anonymoose

    I CAME .357 SIG.

  • alex

    lolz, nato mud

  • Duray

    Everyone is hating on the 9.5″brake, but it’s not like 16″ of barrel would do a lot for you. Velocity increase from 6 inches to 16 looks like about 100fps or so in 9 or 40 cal, and accuracy shouldn’t be appreciably different.

  • Pingback: Glock Forum » SIG MPX Submachine Gun 9mm NATO, .357SIG and .40 S&W()

  • Hedd Wyn

    Please make this in 10mm Auto.

  • Ivan Tsirkov

    Definitely not the world’s first SMG firing from a closed bolt, gas-operated, and using a rotating bolt for locking. Two examples off the top of my head:

    H&K MP7 (Some might argue that it’s a PDW and not a SMG)

    The Russian SR-2:

  • Anomanom

    What, if anyone knows, is “NATO Mud.” Is it some sort of regulation battlefield mud?

  • Pingback: Aftermath Gun Club | Custom 9mm AR15 SBR Thoughts()

  • Pingback: New SIG MCX PDW | State Of Tactical()