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MPX FTE/Double Feed Issues - Input Requested


fbzero

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Hello,

 

I'm reaching out for assistance in troubleshooting an ongoing problem with my MPX(Competition/Gen2.5).  Unfortunately, the problem has been hard to duplicate for diagnosis.  It only seems to happen on the timer, so I'm usually in a rush to clear it instead of diagnose it.  Even more frustrating, it has generally run 100% at local matches, and only seems to do this at bigger matches(just my luck!).

 

Basically, it ends up with either two rounds in the chamber area or possibly one round and one case that may have failed to eject.  I'm not sure which since it's always in the clock, I just know that in each occurrence the RO's have told me that they saw two pieces of brass come out when I got the mag stripped and racked the bolt a few times.  The most recent time, the magazine was also very hard to strip when this happened.  From memory, I think it has happened more often than not with a magazine with a TTI extension on it, stock spring.

 

Obviously I know I'm not giving much to go on as far as an exact diagnosis here, so I'll just make it a more simple with a couple questions; Did those of you who have these MPX's running reliably change anything in regards to extraction to get it there?  Most people I've seen suggest extra power springs for magazines with extensions described the problems encountered as failure to lock back on the last round...could a magazine spring that is too weak cause the type of failures I am getting?  

 

TIA!

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How often do you clean the gas system?

 

Put in the TTI extra power spring for the +11 extensions

 

When have you last changed the extractor spring?

 

How often do you clean behind the extractor?

 

What is your ammo load data?

 

I assume you had a failure to extract that was jammed up with a loaded round. This would cause the loaded round to be stuck on the magazine feed lips causing you issues to drop the mag out. 

Edited by Bdh821
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Thanks for the reply Bdh821; I actually just saw some of your videos on YT the other day, good shooting!  In response to your questions...

 

 

How often do you clean the gas system?  I'd say that I probably don't have any more than 2K rounds through it so far after the most recent match and that I last cleaned the gas system around 1K.

 

Put in the TTI extra power spring for the +11 extensions - Figured this would be worth doing if for no other reason than to avoid lock back issues, just couldn't think of how it might cause this type of malfunction.

 

When have you last changed the extractor spring?  I haven't even taken it apart that far to date, though after this last round of issues at a match, I intend to do so and look for any obvious problems.  Figured I'd probably change it at the same time just to be thorough whether I see any issues or not.

 

How often do you clean behind the extractor?  By "behind", do you mean the part that grabs onto the rim of the cases to pull them out of the chamber?  If so, I'd say every 2-3 local matches(~150 round count each), and always before anything bigger.

 

What is your ammo load data?  Usually I shoot 135gr Blues over 3.5gr Sport Pistol, but they were pretty back-ordered last time I needed projectiles.  This last match, I had one malfunction with 124gr S&B factory ammunition followed by one malfunction with 125gr DG bullets over 3.9gr Sport Pistol.  I did not mix the ammunition in the magazines; Once I didn't have enough of the factory ammo to finish a stage, I loaded up with just the reloads.

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This covers  99.99% of the MPX issues:

 

1. How often do you clean the gas system= gas plug has an expansion chamber when that fills up with Carbon/Lead/Poly Coating  you are reducing the volume and delay to extraction. I.E you are attempting to extract while the case is still expanded against the chamber walls

 

2.When have you last changed the extractor spring= see #1 above this adds stress to the extractor spring and overworks it reducing the extractor springs ability to  maintain grip on the cartage case

 

3. How often do you clean behind the extractor= build up of Carbon/Poly Coating reduces the extractor springs ability to move and maintain grip on the cartage case

 

 Usually I shoot 135gr Blues over 3.5gr Sport Pistol=Coated bullets are bad for the gas plug expansion chamber see #1 above… to use them your clean out on the gas plug would need to be every 200-300 rounds.. I never had good results with Sport Pistol fast burn rate powders fill the gas plug expansion chamber to fast and start the extraction process while the case is still expanded against the chamber walls see #2 above. MPX is better off with medium burn rate powders N330,N340,CFE pistol..

 

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Agree with lots of what’s posted here. 
 

I find the MPX prefers a heavier projectile (124gr or over) and slower powders. I had much better luck with CFE pistol and Shooters World Auto Pistol, than sport pistol (which is my goto powder for carry optics). 
 

If it is indeed prematurely unlocking, and sport pistol is all you’ve got... might consider the +20% recoil springs that are available. Could add a few ms to that dwell time. 

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16 hours ago, Dirty_J said:

Agree with lots of what’s posted here. 
 

I find the MPX prefers a heavier projectile (124gr or over) and slower powders. I had much better luck with CFE pistol and Shooters World Auto Pistol, than sport pistol (which is my goto powder for carry optics). 
 

If it is indeed prematurely unlocking, and sport pistol is all you’ve got... might consider the +20% recoil springs that are available. Could add a few ms to that dwell time. 

Don't agree with the heaver bullets use  115gr @1360FPS /156PF as the easiest bullets to source right now. Had a wonderful 100gr @1520FPS / 152PF load but cant source the bullets again, same with a Montana Gould 95gr JHP @ 1550FPS / 147PF not being made right now..

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I shot 10’s of thousands of factory 115’s... around 152pf... and they were great. Gun was perfect. And then all of the sudden... random FTE’s with them. 
 

Heavier bullet. Slower powders. All helping with that dwell time. 
 

Lena’s shooting 147’s @ 133PF. Gotta be something to that. 
 

I’d personally save the 100’s and 115’s for the blowback guns. 

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Lena told me she shoots whatever is given to her.

 

I shoot 115s with 4.5gr of Sport Pistol which is about 140pf. I use either plated or FMJs. I do NOT use painted bullets
 

Basically the gun needs to have the entire gas system cleaned regularly to be reliable. What does that mean?  Every 6-800rds is what I do. I’ll wipe down the BCG every 3-400 and oil. I’ll take the extractor off the bolt and clean behind there every 3-400 also. Other than mid Atlantic, which I’ll consider an anomaly, my MPXs don't malfunction. 

Edited by Bdh821
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Hey All,

 

Just wanted to say thanks for all the feedback.  Been a crazy busy week at work and this coming week isn't looking any better, so troubleshooting this is temporarily on the back-burner for now.  When I do get to take a look, I'm going to start with a complete disassembly and cleaning and pay attention to the extractor, springs, etc to see if anything doesn't seem right.  After that, I'll stick to factory FMJ's to see if the problem reoccurs or not.

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