Rebuttal: Suppressed SIG MPX Can Spit Back In Your Face

When James’ video about suppressed MPXs not having blowback was posted I watched it and immediately emailed him that I personally have experienced a suppressed SIG MPX violently spit back in my face. Why and how does this happen? As far as I can tell, it happens with a particular set up. Specifically a SilencerCo Octane 9 on an 8 inch MPX. Others may have experienced significant blow back with their setups. But this is the one I have tried and know it will always spit back.

I had my friend put his brace back on his SBR for a comparison of braces for another article. I also put his Octane 9 on the collapsible braced MPX as it is a Gen 2 MPX to see if there is a difference. There was no appreciable difference.


Since the collapsing brace has a shorter LOP, my face was closer to the MPX. With the regular brace I could pull my face back a bit and alleviate the problem.

I tried to mimic James’ napkin collection method. However there was nothing found on the napkin. When I removed the napkin I could feel the blow back on my face.

When shooting somewhat rapidly, pressure builds up rather quickly from the Octane 9 and I can feel powder stinging me in the face and lips. It is worse than just gas to the face. Stung eyes from gas and smoke is one thing, but being pelted in the face is unpleasant.

Now when we ran my friend’s SilencerCo Osprey 45 on the MPXs there was little to no gas and no flying debris.

I was using Browning 115gr FMJ 9mm ammo and have experienced similar results before with other 9mm 115gr ammo. I have not had a chance to try other ammo like subsonic ammo. Perhaps with sub sonic there will be less back pressure and less blockback with the Octane 9 setup? My friend Corey said that he has experienced the same results when shooting 115gr Remington and 147gr American Eagle sub sonic ammo. He also has a second MPX with a chopped down 4.5″ barrel and experiences the same amount of blowback with the Octane 9.

Unfortunately the only way to know if an MPX will get blow back suppressed is to try it and shoot it.  Easier said than done. Best thing to do is do your research and see what other people have run successfully on their MPXs.

Nicholas C

Co-Founder of KRISSTALK forums, an owner’s support group and all things KRISS Vector related. Nick found his passion through competitive shooting while living in NY. He participates in USPSA and 3Gun. He loves all things that shoots and flashlights. Really really bright flashlights.

Any questions please email him at


  • G B

    Why is there so much discussion and attention on this subject without any of the people stirring it taking the time to consider/test all the different variables? Making a Youtube video and a blog post on TFB without trying anything other than 115gr ammo? Are you kidding? I hate to sound hateful but it really is disappointing and it does tend to perpetuate rumors and spread false assumptions. From a few of the different types of ammo that I’ve tried I can tell you that what ammo you choose matters a ton, even the humidity and wind can have a pretty considerable effect on how much gas to face the shooter feels.

    As for my personal data points I can say that I’ve experienced little to no gas to face with Freedom Munitions 115gr RN New, Freedom Munitions 147gr RN New, Federal American Eagle 124gr FMJ Suppressor. I’ve also experienced a TON of gas to face with Winchester “White Box” 115gr FMJ. My friends have shot some other types of ammo through it but I wasn’t behind the trigger to feel what it felt like.

    My setup is a Gen 2 MPX 8″ pistol with a SilencerCo Octane 9 HD using a Griffin Armament fixed barrel spacer. Still waiting on my beloved friends at the NFA branch for an approved Form 1.

    • JumpIf NotZero

      I think worse are the people that are just straight up using annecdotes as “proof” of something not existing becaus it’s likely they just don’t notice.

      There are too many people who notice bad blowback on the MPX to ignore. Smoke-Fire.

    • Nicholas C

      I did claim that this specific setup had these issues. Are you running nose to charging handle on your MPX? If you pull your face back a bit you don’t get as much gas to the face.

      • G B

        I shoot pretty close to charging handle. In my experience a suppressed MPX can be either a real joy to shoot or a tear jerker that you have to hold your breath to shoot by changing nothing but the ammo. My point in this comment as well as my comment on the “mythbusting” Youtube video about a week ago is that the ammo being used is very important and neither of the two “tests” even bothers to try different types of ammo on the same day, with the same set up, the same shooter, etc.

        • Nicholas C

          I asked the owner of the can and MPX if he has tried different ammo. He has and same result.

          • G B

            I don’t know the owner so I’ll assume that he probably just hasn’t tried enough of a variety of ammunition to notice a difference . However, at least in the case of my MPX and my Octane 9, anyone who says that there isn’t a significant difference between shooting it with Freedom Munitions 147gr RN and Winchester white box 115gr is just pulling your leg. Either way I would think you would want to test and verify for yourself when writing a rebuttal for a very popular news/blogging website.

            By the way, the difference has been noticeable to lots of new shooters as well. Usually my friends/coworkers that have never shot before will pick up some ammo from Walmart on the way over to try to pitch in some. It’s almost always Winchester 115gr. When they first load up a mag and try the MPX suppressed they will get a confused teary eyed look on their face that says what the heck is this thing and why would you want one. All I have to do is swap out their Winchester 115’s with some of the Freedom Munitions 147’s or some American Eagle subsonic 124’s and then stand back and watch their faces start to grin. Some giggle a little, but I don’t judge.

          • Nicholas C

            I will let him know about the Freedom Munitions 147s. He runs American eagle 147s and gets gas to the face.

  • NineWays

    Backpressure is a thing with the Octane. I get residue in the face with a Walther P22, Glock 17, and 10″ AR-15 in 9mm when I use almost any factory ammo. With Subsonic 124gr handloads in the 9mms, I get essentially none.

  • thedonn007

    I just used my 9mm Octane this weekend with my 4.5″ barrel 9mm AR-15. I used freedom munitions 115gr blaster and reloaded 147gr. I did not experience any blow back.

    • Nicholas C

      Thats great. But your 9mm AR is not a 4.5″ MPX. My friend Corey also has a 4.5″ MPX and it still spits back in his face when running his Octane 9.

      • thedonn007

        Sorry, just trying to provide a point of reference as we used the same suppressor.

    • spotr

      Most of the AR-15 9mm designs are straight blowback guns with a heavy bolt.
      The Sig MPX uses a gas sysyem to cycle the bolt, so there is always going to be more gas coming out of the back of this gun.
      It’s not the only issue, but I believe that this is one of the major factors for the gas-to-face MPX videos.

  • JumpIf NotZero

    The “napkin” method is ridiculous. That’s only going to work on a pistol can where there is a lot of lube on the action and fully exposed moving parts. Yes the MPX has lots of blowback. No, most people don’t know what they are even looking/feeling for apparently even some self-proclaimed experts, it’s like TV black levels – once you know what it is, you can’t unsee it.

    The action opening too early is a feel in your face/eye/shoulder, a smell, a look, and a sound.

    The MPX was a cool idea – but it’s a 9mm AR and despite being piston has all the issues of a typical 9mm AR.

    • Gorilla Biscuit

      I wanna know if you can shoot +p+ or 40,000-50,000ish psi loads in the gun, with the rotating bolt set up.

  • Jakewwa

    If I read correctly, there is a noticeable difference between different suppressors? One is 9mm the other .45? The .45 no blowback? I think the answer is written.

    • Nicholas C

      Not necessarily. I would like to try a Octane 45 and an Osprey 9 to see if those make a difference.

      • Budogunner

        It definitely would. I run a .45 suppressor on 9mm hosts for this reason. It won’t be as quiet but the over-bore makes blowback a non-issue.

  • Anon

    Correct me if I’m wrong, but the Scorpion EVO isn’t known for having gas blowback issues, right?

    • The Scorpion EVO is very suppressor friendly. It certainly gets points there.

      • Anon

        And it’s simpler than a MP5 or MPX in its operation, for better or worse, because blowback operated guns have less moving parts than a roller-delayed blowback or short-stroke gas piston gun.

        For better because you don’t have to worry about the rollers wearing out or whatever on a blowback operated gun, and for worse because it shoots less “smoothly”, isn’t as great of a suppressor host, and requires the gun to be heavier (not that it’s unacceptable like the Thompson or MP 40 is).

    • Nicholas C

      None that I have noticed but I have only tried a Griffin Armament Optimus on mine

    • spotr

      The scorpion evo is a straight blowback gun with a heavy bolt.
      The Sig MPX uses a gas sysyem (like an altered AR 15 design) to cycle the bolt, so there is always going to be more gas coming out of the back of this gun if compared to a heavy bolt blowback design.

      • Anon

        Why did they think that using a short-stroke gas piston for a gun was necessary anyway?

        Blowback or roller-delayed blowback always just worked fine for SMGs, so why use that, and why keep that charging handle if the damn thing’s going to be proprietary?

        • FightFireJay

          Lighter weight than a straight blow back and potentially easier to produce or less maintenance failure compared to roller delayed.

          • Anon

            The weight thing isn’t that big of a deal for SMGs anyway, so it seems to me like it’s a solution to a problem that didn’t exist.

        • Nicholas C

          The charging handle has always been a major issue for me. I concur, if you are starting a gun from the ground up then why keep a rear charging handle?

          The excuse many give is for the sake of Manual of Arms. People who are used to AR15s will not be confused with the MPX I call BS. People that familiar with AR15s should probably have shot an MP5 at some point in their lives. Who honestly would get confused when SHTF and try to reach back for a rear charging handle on an MP5? No one.

          • Dual sport

            Are you being sarcastic? I can’t tell but I can tell you that one training to the point of doing something on reflex will most certainly present you or anyone else with that type of situation. It’s how the mind works.

            I suspect Sig built the MP10 with that manual of arms as a marketing tool. I agree that I would have dumped the charging handle if the above were not my goal.

          • CommonSense23

            Have you ever carried a gun for a living? Had to use one outside of a range. The AR15 charging handle is excellent.

  • AndyT

    I imagine a can with a large blast chamber would have lower “back blast”, but higher first round pop. I don’t have a mpx but I do have a form 1 can designed with a large blast chamber to limit the blowback on my 9mm ar as opposed to my AAC tirant 9.

  • Marc

    One reason why I hate the AR rear charging handle.

  • Anonymoose


  • Greg Richards

    man up