I was having reliability issues that I thought were related to my gas system: http://www.ar15.com/forums/t_6_45/476166_MPX-Short-stroking-.html

So I ordered a new barrel/gas block from ILWT hoping that would fix it. I was having the same issues with the new barrel so I contacted ILWT and Rob told me to send him my upper so he could check it out. Rob had the upper for a week or so and put several hundred rounds of various ammo through it to diagnose the problem. It was very clear from the time he spent and his almost daily communication with me that I was a priority for him, and he was aware from the get-go that there was almost zero chance that the problem was related to his products. My main point in posting this is that this was by far the BEST "customer service" experience I have ever had with any product. This was all done at no charge, BTW.

It turned out that for whatever reason, my particular gun just needs more gas so he opened up the gas ports a bit more to .0625. The main culprit however was the extractor spring. For some reason my gun came from the factory with only the extractor spring installed; no rubber/polymer insert inside the spring. For the first few hundred rounds I shot through the gun it worked fine, but apparently over time the spring took a set and was just too weak to extract. The spring was visibly shorter than a spring with the insert and it was very weak. I was having double feeds and empty cases left in the chamber which I interpreted as the bolt not cycling far enough to clear the spent cases, but it was really the extractor.

Not having a spare Sig spring, they fitted an AR spring in the bolt and it ran flawlessly for them and for the few rounds I've been able to shoot since I got it back. So I guess this is at least a stop-gap option if anyone is having similar issues. I ordered a couple of spares from Sig and although I just got a a total, not unit price, I think they were about $7-9 each.

If anyone is in the market for an MPX barrel or other part made by ILWT, all I can say is buy with confidence from them because they will not only stand behind their own products but are willing to help their customers even if their own parts aren't at fault, which is rare I think.

I too am impressed with how Rob helped me with a 3-lug issue.

Prib

I am very pleased with the MPX barrel and gas block I got from ILWT as well.  Good folks to deal with.

Awesome! Glad you finally figured out the problem!

By chance, do you have Sig's part numbers for the springs? I like to keep extra parts handy just incase something comes up.

What was the issue?