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Sig MPX problems

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For my MPX, I had similar gas/ejection issues in stock form.  I like 147s and wanted to keep the load the same for pistol and rifle so I ended up on this:

147 Plated (doesnt really matter which ones but I've lately used Everglades RN)

3.3 gn N320



To get this to run reliably:

-Gas port enlargement (for Gen2) by ILWT

-'Open' gas plug by ILWT

-Make sure your mag springs have enough tension - I had issues with the Taran basepads so I only use Taylor Freelance

-Make sure the gas port is clean enough to allow the tappet to move freely without too* much force.  I highlight this because the tappet will always need some resistance, it shouldnt just slide right in and out.


Verdict is still out but my MPX Gen 2 reminds me a lot of certain open guns - it takes some work to get it dialed in, once you do that, its just a matter of maintenance and checks.

Hope this helps.


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I think they're fine really. The Gen 1's seem to have less issues, but only because they came with a more open gas port. Then all the Tactical Timmies (who buy WAY more MPX's than USPSA/3-gun PCC guys) complained about gas to the face.


So now we have a Gen 2 that.... ta-da, doesn't like mouse-fart loads with fast burning powders. It was designed to run on factory 1100+ fps 115gr to 147gr 150+ PF loads, not 3-3.2 of TF under a coated 147. So your options become... have ILWT make it a de-facto Gen 1 (Tune your gun to your ammo) OR.... tune your ammo to your gun.


Refusing to change one or the other isn't really the gun's fault. Also, yes, they like to be kept clean and it's an incredibly simple process. 

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In my experience shooting one in competition for the last year, having problems with it, and seeking advice, you need to run ammo with a power factor above 130. (Google how to calculate power factor if you don't know how to do that.)  When I discovered that, my issues with not cycling and double feeds were gone.

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