Need help with MPX FTE/Stovepipe Issues

[k2pichu]

Gun: SIG MPX PCC Competition/Gen 3.

 

Issue: Failure to eject/Stovepipe. The spent casing is extracted, but doesn't eject causing the next round to jam up. 

 

Round count: I purchased a new MPX 8 months ago and have about 8-9k rounds through it. I've experienced hundreds of these malfunctions, all identical. The malfs occurred fairly early on, but I didn't know enough about firearms at the time to realize it was not normal at the rate I was experiencing them. 

 

Mods: MPX is stock except for the Radian charging handle, grips, red dot, and magwell.

 

Thing's I've noticed: Inconsistent ejection, both in direction and distance. Sometimes the casing is sent 5-7 yards away at 1:30, Other times, it dribbles out 1-2 yards away at 3:30. The eject cases seem to be spinning a lot. The orientation of the jams also seem to indicate the case is spinning more than it is being sent out of the port. The anondizing/paint is worn on the inside of my upper receiver. 

I seem to have around a 1% malfunction rate. It's often enough to occur almost every match, but not often enough to easily debug. I've participated in about a dozen local matches this year and have had at least one malfunction in two thirds of them. I've done two majors and had malfunctions at both of them. 

 

Cleaner and Lube: Hoppes 9 cleaner, Hoppes Elite Cleaner, C4 Boretech carbon remover, Hoppe's elite oil

 

Troubleshooting so far:

• Read all the forum posts and internet resources on this issue
• Fully cleaned and lube BCG/Upper receiver and cleaned gas system, checked correct gas plug depth. Still malf within 50-200 rounds. 
• Mix of 115/124g FMJ factory new brass from Blazer, Federal American Eagle, Sellier and Bellot, and Fiocchi. Malf experienced with all brand/project weight combinations I've tried. I also tried Brian's MPX GM Loads but had 2 malfs at that at Area 7.
• Different (all Lancer) magazines. Malfunctions occurrence is spaced out in the mag. Sometimes it's happens in the first few rounds, sometime at the end, with no observable pattern. I tried brand new magazines with no real improvement.
• New Gas plug + tappet from ILWT. Installed this before Area 7, 20 rounds of zeroing, two malf's in first 5 stages. No malfs in second 5 stages.
• New extractor and spring, rubber insert, and donut o ring from ILWT. Experienced malfs within 100 rounds. 
• Sent back to Sig for warranty, the customer service agent was friendly and the gunsmith replaced the extractor and spring. Malf within 30 rounds, 3 more malf's in the next 350 rounds during practice. 2 malfs experienced at Area 7 (~350 rounds). 
• Sent back to Sig again for warranty, they told me they shot another 60 rounds and saw consistent ejection pattern and that the malfunctions were caused by user error. The same customer service agent I talked to suggested I had a "limp shoulder" ("limp wrist", but for rifles???) and that I should try shooting other people's MPX to see if I get the malfunction there and have other people shoot my MPX to see if it happens to them. Makes sense to eliminate the variable of the shooter vs gun, but logistically and cost wise that's not really practical. On the call, the customer service agent seemed very annoyed at me and pretty much told me to f*#k off and if I tried to send it back they would charge me for shipping, gunsmith time at $75/hr and ammo used. 

I'm honestly out of ideas at this point and tired of trying to debug this thing. I know ILWT sells and adjustable gas plug and variable spring rates, but I have no clue if my problem is too much gas or too little gas or what direction to even go in. With my tests and discussions with other local MPX users, I'm confident my issue is not with cleaning or ammo related. 

 

Depending on the price and cost, I'm considering:

• Buying a new upper assembly. Ideally I buy just the part that's not working, but I don't know how to tell if it's the receiver, BCG, or gas system on the barrel that's causing the issue. 
• Selling my MPX and buying a new one. I've never done this before and don't have any idea on the process, valuation, and laws surrounding this so I'm a bit weary of this option. Depending on how much I can sell it for, it might be more cost effective than buying a new upper assembly. I've invested a lot into this platform with magazines, loader, mag carrier, etc. and I really enjoy the platform so I'd prefer to stay with the MPX if possible, I just don't know what to do to make it reliable.
• Sending it to the ILWT guy to see if he can gunsmith a solution to this. I don't know what the problem is and I'm not sure if he offers services for this or not.

 

Link to pictures: https://drive.google.com/drive/folders/1e3LH4-6kmrcGPKEbwNRV3MOENZ8SKLYO?usp=sharing

 

If you guys have any additional insight or suggestions, it would be greatly appreciated. Thanks!
 

[Dirty_J]

This is exactly why I got OUT of the MPX platform. Loved the way it shot. Random FTE’s developed at around the 10k round point… maybe 1 every 300-400 rounds. Too expensive to shoot the ammo to chase it down. Just frequent enough to wreck a major match. 
 

+power recoil springs, reduced power recoil springs. Extractor. Extractor springs. Plus power extractor springs.  New tappet. New rings. 

 

No amount of part swaps could get it back to 100%. So off it went. 
 

 

Edited September 17, 2022 by Dirty_J

[texasdawg]

 It seems to me that the problem is gas related, but I'm not 100% sure. On my MPX competition model '21 vintage I have had the ejection/extraction problem also. (Sig seems to be doing a rolling factory upgrade as production goes along, so your millage may vary). 

 I have in mine the factory Sig barrel's gas port drilled out to .065". I use a ILWT adjustable gas block on the most open setting(.065") and clean the gas system every 2nd usage.. I use xtra power AR15 extractor springs with the spacer and donut changed out every 1500 rounds or so(monthly). I use the ILWT +20% recoil springs and I shoot 135PF 124gr RN FMJ bullets with Shooters World major powder for the gas production. All these changes have reduced my malfunctions to about 1 every 1K or so, but it usually is at a match and not at practice. I've got the clearing down to about 11 seconds or so, but that is forever at a match. (not smiley face emoji !)

 The MPX is a better shooting gun(accuracy and smoothness) than my franken' AR9 blowback gun, but it stays as my backup gun at a match because the AR9 goes bang every time. I should have just built another AR9,,,

 P.S. the ILWT guy is a great resource for help, but is not competition oriented,,,

[Orlandoech]

On 9/16/2022 at 9:51 PM, Dirty_J said:

This is exactly why I got OUT of the MPX platform. Loved the way it shot. Random FTE’s developed at around the 10k round point… maybe 1 every 300-400 rounds. Too expensive to shoot the ammo to chase it down. Just frequent enough to wreck a major match. 
 

+power recoil springs, reduced power recoil springs. Extractor. Extractor springs. Plus power extractor springs.  New tappet. New rings. 

 

No amount of part swaps could get it back to 100%. So off it went. 
 

 

Same here. After 5 months of this I called it a day and sold my MPX to a friend that plinks. It was a nightmare. 
 

I went to a Brekke PCC and experienced 0 malfunctions so far. DB or RDB is the way to go. 

[drdre352]

I would try changing out the extractor springs. That was issue with the one I had.

[k2pichu]

If you read the original post, the extractor and springs were changed multiple times as part of the debugging process with no noticeable effect on reliablility. I ended up changing the MPX to a JP5 and it's been 100% flawless since. 

[Salsantini]

I would contact Rob at ILWT.  Explain you issue.  He would be the best person to discuss this with.  

[k2pichu]

I did contact Rob but we did not find a solution without doing permanent mods(gas port opening). Trust me, I tried everything and asked everyone locally that shoots an mpx. Selling it and buying a jp5 is the way.

[Smokey99]

I tried all of the above fixes and have the failure to eject (empty case hung up over partially fed round. the upper and rear edges  of ejection port are heavily dinged from brass strikes. Two things come to mind: 1) open up the upper and rear portions of the ejection port, and 2) Tune the ejector similar to how the problem is resolved on a 1911 .45 acp. There is a MPX "Gen III" Upper Receiver that has a different ejector - wonder why?? Will the Gen III work on the Gen II lower??

[k2pichu]

If you're just shooting PCC for fun and enjoy gunsmithing, there's nothing wrong with modding it to see if you can come up with a solution, but if you plan on competing seriously in PCC, I'd just sell it and buy something else. The time you spend tinkering and the money you spend on parts and ammo while testing easily allows you to just buy a more reliable PCC.