We are big fans, in theory, of the SIG MPX. We’ve been following the saga of the gun itself, and of the company’s battle (a losing battle, so far) to get their innovative muzzle-brake-converts-to-suppressor-with-a-registered-tube version approved by ATF. We like the look of this modernized take on the MP5 form factor, and now people are starting to get them out in the field. And that, as Art Spiegelman wrote of his dad’s experiences, is where the troubles began.
Bearing Arms had a report on a problem with a production MPX. The problem was experienced by a guy named Darrell with a YouTube channel he calls “Tactical Existence” (really?); his tagline (gagline?) is: “Tactical is not just a word it’s mindset & a lifestyle.” (Punctuation his).
You don’t say.
Anyway, the guy’s website has the MPX video at the top. However, he does not show the MPX malfunctioning out of concern for his own liberty.1 Initially, he loved the MPX, firing it with the SIG Brace against his cheek and fastened to his arm. But then it began to double on him. His explanation:
We started with a fresh case of PMC 9mm brass ammo, and much to our surprise the gun almost immediately started to have serious malfunctions. At first we weren’t sure if the guns having some weird sort of bumpfire situation, or if it was something more serious like a double fire. After running a few quick test there was no doubt that the gun was in fact having a double fire malfunction. The weapon would fire with a pull of the trigger and then again on the reset of the trigger. this is a big problem because as most of you already know if you are in possession of a firearm that fires more then one round with a single pull of the trigger it’s your fault no matter if it is or not, well in the eyes of the ATF anyway.
That’s a reference to US v. Olofson, right there, although he might not know the name of the case he understands its legal import. And that’s why his video isn’t embedded here — since it doesn’t show the failures, it’s not really of interest to us, but we understand why he didn’t want to put incriminating evidence, at least as the ATF sees it, on the web.
The cause of the double-fire was a bit unusual:
After figuring out that we had an issue I took the lower receiver off the gun to inspect the trigger group. I found that the trigger group pins had walked out of the gun and was causing the hammer not to catch the disconnector. We then put the pin back in the gun and test fired to see if this fixed the problem, which it did for a second anyway. After about 20-25 rounds both trigger group pins were starting to walk out of the receiver again, at this point we stopped shooting the gun and called Sig for repair.
We’re not really sure how you fail to notice the pins walking out of the gun in the first place. The original AR-15 trigger module design used the springs themselves, riding in grooves in the pins, to retain the pins and was very effective at doing that. People who’ve had pins walk have usually had grooveless pins, the el cheapo kind.
Here is a video showing the trigger mechanism of another guy’s MPX at about 3:22 to about 3:50. At 3:36 you can see two pins, one of which has faint grooves and one, no grooves at all, in the upper left quadrant of the video. (We’ve cued it up to start at 3:02. You can wind it back if you want the whole thing).
This guy had the trigger mechanism out to replace the trigger spring with a lighter one, to reduce the trigger pull.
The MPX enters a crowded market for 9mm carbines and submachine guns. (The gun’s original design concept was a product-improved MP5). It’s not the market’s incumbent entry (that position is held in the LE market by the MP5, still marketed in a desultory way by HKUSA, and in the civilian market by 9mm AR clones), and it’s not the low cost entry (that would be the CZ Skorpion Evo, less than half of what scalpers are getting for MPXes right now, and with mags perhaps 1/4 of the SIG’s Lancer polymer mags). So it’s vital for SIG to get this right.
The modular rifle-caliber suppressor-host SIG MCX, which shares some components and concepts with the pistol-caliber MPX, has also had, in some examples, feeding problems. This suggests SIG still struggles with QC, but seems completely unrelated to the walking pins in this one example of the MPX.
The fanboys at SIGForum.com have been watching this for some time. This link picks up the MPX thread on p.24 in March and you can continue forward from there, including a discussion of the Tactical Existence report. Several forum members have fired more rounds that Darrell managed to do, and none have had walking pins. A more common problem cited by the forum members is a complete lack of spare mags, so far.
- Darrell is thinking, no doubt, of US v. Olofson, where a guy was convicted for a gun that ATF SSA Jody Keeku and the amateur gunsmiths of Firearms Technology Branch spent four months massaging; they bubba’d it until it doubled 50% of the time. David Olofson spent several years behind bars (he’s been out for years now, but he’s a felon forever). Showing the MPX doubling would be giving the ATF all the evidence they need to throw Darrell in prison on the Olofson precedent, not that they really pay any attention to precedents.