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Sig MPX won't fire more than one rd at a time


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I hate (NOT!) spending other peoples money, but the MPX is a dirty girl, so I have a spare gas piston, spare gas valve, and a spare bolt.  When I clean the gun, I put the clean spares in and drop the dirty parts in the ultrasonic cleaner.  Once they are clean, they go in the spares kit in my range bag.  If I wasn't so cheap, I would just get a spare MPX.....but then I would have twice as much cleaning to do.

 

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Before you go too crazy trying to track it down, maybe just check the cam-pin, make sure the bolt is slick and the piston is dry, and run a little  factory 140ish pf stuff to see what it does..?

I treat mine terribly and hardly clean it but I usually run stuff that’d be above 130pf out of a pistol, so probably more like 140-145ish pf... just guessing but I think the hotter stuff might help in blowing crap out of the gas system that might otherwise become an issue...

 

IDK, just any easy one that might be worth a try?

Good luck.

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On 4/16/2020 at 9:19 PM, Gregg K said:

Did you ever check the orientation of your cam pin?

 

Bolt.jpg

My MPX has this and I learned the hard way. My gf’s MPX is newer, both are a MPX competition, and her camming pin is ambidextrous. Idk if that’s the right term for it. Now that I think of it a local shooting friends is also ambi. 

 

I purchased a backup bolt carrier group I guess you could call it from ILWT. It also has an ambi cam pin

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At FL state I had the issues as described, no light strikes, pull the trigger & hear a ‘click’ which I assumed is the hammer falling but nothing.  After finally taking it  apart & cleaning I took it to the range recently & that’s when it would fire once but not a second time unless I cycled the bolt, this is also where I noticed the bolt not completing closing some times which I know won’t allow the gun to fire.  But even after recycling to get the bolt to close it would just fire once.  Unfortunately I don’t remember if I checked to see if the bolt was fully closed after it fired.  If it was not each time then I agree that’s clearly the problem.

I’m going to disable it today & check the gas port and then bring it to the range tomorrow to see where I am.  I just cycled the bolt a few times & it fully closes each time now so we’ll see..

 

I may have to start cleaning the gas port more than every 800 -1,000 rods?

 

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On 4/16/2020 at 9:19 PM, Gregg K said:

Did you ever check the orientation of your cam pin?

 

Bolt.jpg

Yes, that’s how I have it as well ....

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Appreciate all the feedback guys & Im not ignoring anyone - just others things are taking priority these last few weeks - no shooting since march - can’t actually remember the last time I didn’t Shoot for 4 weeks straight .....

 

I’m going to check the gas port today, lube the bolt a little more on the outside and then try it tomorrow & report back ...

 

 

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Posted (edited)

Ok, 99% sure what the issue was ...

 

took the gun apart and the gas tappit was basically frozen in the gas port :(

took a soaking in Hopes 9 & a mallet and punch to dislodge ... its currently on my garage floor somewhere :(

luckily I have a spare.  Just don’t remember that many rods thru teh gun since teh last time I took teh tappit out ...?

 

One question, does the gas valve need to be disammbled too?  Looks like you need some kind of ‘special wrench’ to screw off the face of it?

 

cleaned it all reassembled & lubed - bolt closes freely when charging so we’ll see tomorrow if I can get at least 200 rds out of it since our range has decided to restart matches as of 1 May & the steel match is every 1st Saturday.  

 

All sorts of new rules like everyone has to wear a mask and bring cleaner & sanitizer with them to clean after every shooter, etc.  we’ll see how much fun it is - might end up postponing more matches until all this >>>>> subsides

 

Edited by Nimitz
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For my MPX's I have switched to the IN LEAD WE TRUST open gas plug, which basically allows open access from the gas port in the barrel to the gas opening in the block where the plug goes in.  My pistons come out hard as they need to run dry to make the gun run reliably longer.   Running dry seems to go against conventional thought process, however if you lube in there it turns to goo in short order.  Found this out the hard way at a USPSA match.  I would try one of the open gas plugs to see if it makes a difference.  ILWT is a great resource!!!  Good luck and stay safe.

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gun is now running without issue ... I'll look into those open gas plugs in the mean time, thx!

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