SIG MPX failure to eject

[Chillywig]

I have the carbine with ~3000 rounds thru it. Has ran without any issues since switching to wolf steel cased 115gr fmj factory ammo. (My 147 GR reloads were a little weak and would not lock the bolt back on an empty mag)

 

Past two days I have ran into these failures to eject - all exactly the same. The case is not clearing the ejection port and I end up with the fired case sticking out the chamber. The bolt is going back far enough to grab a new round so I end up with the bolt half out of battery holding a live round and the fired case sideways preventing the bolt from closing.

 

After experiencing this a few time yesterday I cleaned the whole gun gas piston ect. I think this was the first time the extractor had been out of the bolt and it was nasty. Carbon built up on the extractor face and inside the bolt. After thoroughly cleaning everything I assumed it was the filth causing the problem and took it out to make sure today. Again had the exact same failure to eject described above.

 

Anyone else been down this road?

 

Thanks 

[TRUBL]

Mmmmmmmmmaybe.........or at least I might be going down that shopping aisle. I will pull mine apart and do an inspection of extractor tension and ejector set up. Will get back to you. Might be a couple days

 

[mach1soldier]

Gen 1 or gen 2? Did you try any other ammo?

[Chillywig]

Gen 2

 

I have fed it other ammo but was feeding it wolf exclusively at the time

[Chillywig]

[Chillywig]

Here is the extractor from my carbine verse pistol Gen 2 MPX

 

Pistol has about 1000 round count

Carbine has about 3000 round count

Edited September 8, 2017 by Chillywig

[sfinney]

http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/

 

This and many other tests show steel case lacquer (or polymer) coated ammo in higher temperature firearms like rifles can cause the coating to come off in the chamber and really mess up chambers causing sticking cases and extraction problems. I ran into this first hand with an AR many years ago....   not sure the MPX would do the same thing, but I would thoroughly clean the chamber to remove any varnish, and run with Win or Fed ammo a few hundred rounds to see if the issue repeats. YRMV

[Chillywig]

I called Sig about the extractor spring and was advised it should be replaced every 5 to 10 thousand rounds. I assume since I have been basically shooting steel cased ammo exclusively it takes a bit more force for the case to roll out off the bolt face and puts more tension on the extractor spring. At four dollars each I can swap them out every few thousands rounds.

[Aircooled6racer]

Hello: You could stretch the spring one time to see if that solves the problem. If it does then replace the spring. You can buy lengths of spring and cut them to length needed. Measure the wire diameter and the diameter of the spring to get something close. Thanks, Eric

[DocMedic]

First completely strip the MPX down and clean all the parts to include taking apart the gas system. If you can pressure wash the inside of the upper receiver I use a garden hose with a sprayer nob, you will be surprised how much gunk is actually stored in the upper receiver. After you spray it clean go ahead and dry and oil it and clean whatever is left. When re-assembling make sure everything in the upper is WELL oiled, barrel, gas piston, etc. On the BCG I make sure that both recoil springs are cleaned and well oiled as well as the plunger, I then use grease on the outer BCG itself. Anywhere the BCG will make contact with the upper you want to make sure is greased. Test fire.

 

If you are still having ejecting issues you might have weak magazine spring issues. If you have a mag that has not been used a lot, try loading it up and test fire, what you want to do is watch how consistent the direction and how far the spent brass is ejecting. If that is fine try your jamming mag and see if it does the same, if it doesn't its time for new springs.

[Nathanb]

Are you sure the gas piston and tapped are in correctly? Make sure it kind of clicks into place.  I had the same issue when it wasn't in properly. 

[Neomet]

Change your extractor spring.  In a pinch I have pulled one from my AR and used it.  

[Chillywig]

I did clean everything including the gas piston assembly first and the problem persisted. Once I swapped the extractor spring the problems went away.

[zdog]

I am having the exact same problem.  My gen 2 was made in Feb, 2017.  Did you ever solve the problem?  I have done all the same things as you and more.  I started to have this problem after about 3 thousand rounds.  A friend at my club has an MPX that does this as well.  Mine happens every 1 or 2 hundred rounds.  Just enough to screw up my match.  Just today I broke down and sent it back to Sig. I am not sure they can do anything with an intermittent problem. I even have a spare barrel with its own gas system that does it too.

[George16]

He said he replaced the extractor spring and the problems went away.

 

“Once I swapped the extractor spring the problems went away.”

[zdog]

4 hours ago, George16 said:

He said he replaced the extractor spring and the problems went away.

 

“Once I swapped the extractor spring the problems went away.”

I have changed the extractor spring, multiple times, but I have also had three different extractors, one was ilwt, installed.  

 

Glad he got it fixed but I am still searching.  I am up to 7000 rounds and my friend claims 20,000.  Maybe I will get lucky and Sig will replace the entire upper.

[George16]

There’s a big chance Sig will just send you a new upper. They had been pretty good in fixing or replacing non-working parts.

[zdog]

7 minutes ago, George16 said:

There’s a big chance Sig will just send you a new upper. They had been pretty good in fixing or replacing non-working parts.

 

Fingers are crossed

[Chillywig]

My gun has run flawless since changing the spring the first time. I replaced it at least one time since then. Gun has to have to be over 10k rounds now. I do keep it very clean and pull the bolt wipe it down and oil just about every time I shoot it. Full detail strip after a thousand rounds or so. I have switched from shooting steel cased cheap Wolf ammo to reloading my own for PCC. What ammo are you using?

On 4/6/2019 at 3:27 AM, zdog said:

I am having the exact same problem.  My gen 2 was made in Feb, 2017.  Did you ever solve the problem?  I have done all the same things as you and more.  I started to have this problem after about 3 thousand rounds.  A friend at my club has an MPX that does this as well.  Mine happens every 1 or 2 hundred rounds.  Just enough to screw up my match.  Just today I broke down and sent it back to Sig. I am not sure they can do anything with an intermittent problem. I even have a spare barrel with its own gas system that does it too.

My gun has run flawless since changing the spring the first time. I replaced it at least one time since then. Gun has to have to be over 10k rounds now. I do keep it very clean and pull the bolt and wipe it down and oil just about every time I shoot it. Full detail strip after a thousand rounds or so. I have switched from shooting steel cased cheap Wolf ammo to reloading my own for PCC. What ammo are you using?

[zdog]

Thanks for taking time to reply.  I do all the same things as you and have tried 3 extractors and more springs than I can recall.  

 

I load my own and use PD 115 and 147 grain fmj bullets over w231 with a power factor of 135. 

 

After talking to Sig they convinced me to send it back to them....in fact they are do to get it today.

 

 

 

 

[Sfisch0311]

From what I have gathered from talking to a bunch of people that have had the same problems, you want to change your load. Slower burning powders are the way to go. A buddy runs 124's with 5.5 gr of HS-6, and that's the load I plan on using when I get my MPX. Those faster powders don't operate the gas system as well, so that could be part of your issue.

[George16]

7 minutes ago, Sfisch0311 said:

From what I have gathered from talking to a bunch of people that have had the same problems, you want to change your load. Slower burning powders are the way to go. A buddy runs 124's with 5.5 gr of HS-6, and that's the load I plan on using when I get my MPX. Those faster powders don't operate the gas system as well, so that could be part of your issue.

Not necessarily true. I had used 4.1 Gr of Winchester  231 and now using 4.0 Gr of Sport Pistol with PD JHP and I didn’t have any problems with FTE until 7149 rounds. It wasn’t due to the load either. It was because the roll pin that keeps the threaded plug in place came out and causing it to unthread and under gas the system.

 

I have a separate thread about this with pictures of the roll pin sticking out. I now have a MPX PCC model and tested it yesterday with my current loads and everything went well. However, i shot 100 of factory federal 115 Gr ammo first and then my reloads.

 

Time will tell though but I’m hopeful it’ll be alright. It’s already soft shooting so I’ll just keep it simple and enjoy shooting the heck out of it .

[GregJ]

3 minutes ago, George16 said:

I had used 4.1 Gr of Winchester  231

 

That is exactly my CO load, under 124gr Zeros.  They also run great in my Gen2 MPX, about 140pf, IIRC.  

[zdog]

42 minutes ago, Sfisch0311 said:

From what I have gathered from talking to a bunch of people that have had the same problems, you want to change your load. Slower burning powders are the way to go. A buddy runs 124's with 5.5 gr of HS-6, and that's the load I plan on using when I get my MPX. Those faster powders don't operate the gas system as well, so that could be part of your issue.

 

You may be right,  I have increased my powder quantity by 8% to where I am .1 grains over the max recommended using 147 fmj and w231 powder..  When I sent my gen 2 back to Sig they changed the gas plug and sent it back with a note that said they fired 150 rounds with bullet weight of 115 to 147 without issues.  Failures are now less frequent and I am hopeful my problem has been solved.

 

I bought a competition gen 2 model  last month and it has be running well and I have  not had problems.  My friend also bought a competition model and he could not shoot the same 147 load as I do without the failure to eject problem.  He had to run 115 grain white box factory ammo to get it to cycle correctly.  He then bought a ILWT barrel and he can now shoot the same load as I do.  That has to be a gas problem in the factory barrel.  That means to me that Sig still has a problem and its kind of hit and miss.

 

 

 

Edited June 4, 2019 by zdog
Spelling

[Sfisch0311]

1 minute ago, George16 said:

Not necessarily true. I had used 4.1 Gr of Winchester  231 and now using 4.0 Gr of Sport Pistol with PD JHP and I didn’t have any problems with FTE until 7149 rounds. It wasn’t due to the load either. It was because the roll pin that keeps the threaded plug in place came out and causing it to unthread and under gas the system.

 

I have a separate thread about this with pictures of the roll pin sticking out. I now have a MPX PCC model and tested it yesterday with my current loads and everything went well. However, i shot 100 of factory federal 115 Gr ammo first and then my reloads.

 

Time will tell though but I’m hopeful it’ll be alright. It’s already soft shooting so I’ll just keep it simple and enjoy shooting the heck out of it .

Fair enough, haha. I'm just going off of what I have heard. I do know that you don't want a low PF load in it at least. You want something that is really going to work that gun. I'm getting a buddies MPX this week that has had all sorts of issues and I am working up a reliable load for it with that HS-6. Can you provide a link to that thread?