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.