I am posting this in attempt to save MPX owners some frustration.
I own an early Gen2 MPX, but have not shot it much. Early on I attributed malfunction problems to the weapon not being "broken in". However, the malfunction in question, dropped extraction failure to eject, never went away after a sufficient frustrating period. After a recent range visit I did decide to look more in depth of the problem. Since my magazines were relatively new I stored them for several days full and proceded to thouroughly cleaning the weapon and piston system. Everything appeared to function correctly. I then ran several snap caps through an extraction test and each time the weapon functioned correctly. Returning to the range the weapon once again failed.
Although, the extractor appeared fine I felt that tension on the extractor arm was weak. I called Sig and was informed that the extractor spring was a normal AR spring. So once again I stripped down the bolt and removed the extractor and spring. Comparing to the spring to another AR spring I noticed that the original MPX spring was indeed shorter than the AR spring. I replaced the MPX spring with the spare AR spring and grommet and headed back to the range. Wouldn't you know it it functioned flawlessly at slow and high rate of fire with multiple types of ammo.
So for MPX owners who are experiencing FTE issues check your extractor springs and good luck. I do have pictures of the malfunction as well as pictures of the original spring if anyone would like comparison.

Thanks for sharing this

Nice , thank you

I would like to see the pics please. I will email you if you do not mind sending to my email. Thanks

I emailed 2 images to compare the springs to your email in your profile.
Sent a second email of the malfunction as well.

Got em. Thank you sir!

Thanks for the info. Can you please send me the pics also.


Cheers.

So out of selfish curiosity has anybody checked their extractor springs and found faulty weak springs? If so, have you replaced those springs and received better performance?
After my contact with SIG I received a replacement spring which was significantly stiffer and more consistent with a standard AT spring.