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Sig MPX problems


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Got a Sig MPX and been waiting 200 days for the Form 1 so just took it out last weekend and had multiple FTE. Using my reloaded competition ammo 147 RN bullet over 3.3 gr Titegroup.

Noticed cases landed within a foot of so from gun with ejection.

Research implies that the gun is "under gassed" never heard that term before. Seems you have to do something with the gas return system but can't find details. Might just need a break in period with higher power ammo but you would think when paying well over $1000 for a gun it should work. I have a CZ Scorpion and it shoots everything.

I was curious if anyone else on here was having similar problems and had a remedy? Searches didn't reveal anything.

Thanks,

MK

Edited by surgdog
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Thanks for the replies. 

How far out does your gun eject the brass? My brass was hitting just to the right of my right foot. Makes me think not enough gas coming back to operate bolt. 

Will follow the recommendations above and shoot higher powered commercial ammo for several 100 rounds but don't see how this would improve my reloads ability to cycle gun. These are the same reloads I use for pistol competition and I'm basically lazy and don't want to do a separate 9 mm load for MPX.

My CZ 75 and Scorpion work great with them.

Have found this problem noted elsewhere but no definitive answer on how to beat it other than "breaking in". At this point with the cost of the gun and the now approved Form 1 have no choice but to continue on. May call Sig after 1st and see if they have any advice.

Thanks everyone and Happy New Year.

M

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As others have said run slightly hotter ammo for @ 250 to 500 rounds.  

I've found mine likes to be run pretty darn wet.  More so than my .223

Even if low round count I would clean the piston assembly.  if it is not moving freely it will mimick being undergassed.

The MPX being piston driven often takes more powder than a blow back like the Scorpion.  It will feel softer, just takes more powder to run the system.

My 147 molys with 2.8 of E3 toss brass 6 feet or so.  This is after 2K rounds 

Edited by Neomet
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OK, here's an update. Got a chance to go to range and shot 250 rounds of 115 gr S&B commercial ammo. Ejected great and no problems.

Then tried my reloads again and there was improvement in that I had no FTE. Ejected brass going a little further. Only minor problem is that not getting last round bolt hold back with the reloads.

Going to go clean it well including the tappet and oil it up good. Will cont to take it out and shoot commercial until confident in its reliability before shooting in competition.

Appreciate everyone's spot on advice.

MK

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The MPX is the same platform as the M-16 and they love to be wet. I always keep the carrier well supplied with silicone grease. Never have a problem with extraction. Using a chamber cleaning tool is the lase thing I do before putting the rifle away.

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When I got back from shooting commercial ammo and cleaned it that gas valve and tappet where filthy and very stiff. After taking apart, cleaning and oiling they feel much looser so I'm hoping this will help. My production load--147 gr xtreme RN bullet over 3.3 Titegroup at 1.160 OAL was shooting better after commercial ammo so hopefully now after a good cleaning it will get even better.

Happy New Year to all.

mk

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  • 2 weeks later...

Having to send my mpx back to sig. have put about 1000 rds through it and haven't had a issue until lately.. it won't cycle any ammo.. shot high power loads and low power loads and nothing.. stripped gun and cleaned it didn't see any issues.. guess we will see when sig takes a look at it.. 

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11 minutes ago, Mulligan03 said:

Having to send my mpx back to sig. have put about 1000 rds through it and haven't had a issue until lately.. it won't cycle any ammo.. shot high power loads and low power loads and nothing.. stripped gun and cleaned it didn't see any issues.. guess we will see when sig takes a look at it.. 

Can you describe what kind of malfunctions you're having?  Have you pulled the gas system apart and cleaned it?

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Yea.. took it all apart.. with 147gr gun fires and casing doesn't Eject, bolt doesn't move at all.. with 115gr the bolt moves enough to pick up another round but spent case remains in chamber and gets caught up every time.. seems to be a gas problem to me but I can't figure out what he problem is 

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2 minutes ago, Mulligan03 said:

Yea.. took it all apart.. with 147gr gun fires and casing doesn't Eject, bolt doesn't move at all.. with 115gr the bolt moves enough to pick up another round but spent case remains in chamber and gets caught up every time.. seems to be a gas problem to me but I can't figure out what he problem is 

Strange that it ran without issue for some period of time and now won't.  Sure sounds like it's not getting enough gas.  Do the gas rings still fit tight when you put the piston and valve back in the cylinder?

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  • 1 year later...
  • 2 weeks later...
On 1/13/2017 at 9:10 PM, Mulligan03 said:

Yea.. took it all apart.. with 147gr gun fires and casing doesn't Eject, bolt doesn't move at all.. with 115gr the bolt moves enough to pick up another round but spent case remains in chamber and gets caught up every time.. seems to be a gas problem to me but I can't figure out what he problem is 

Funny enough mine did the same thing. I had a cracked bolt carrier. Sent it back they replaced it and now it doesn’t run. I have yet to tackle it to see why. Thing are everything before. 

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I had an issue with reloads as well. Factory ammo ran fine. I had some flat point bullets that the MPX didn't like. I came home and measured the factory ammo. Winchester White Box and Federal Champion are the factory loads that worked, both in 115 grain weights. I ended up using a COAL of 1.156-1.158". It seemed as the new gun light a longer COAL. I haven't tried a shorter COAL since to see if the problem still exists.

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