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Odd MPX problem


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Last Saturday, I shot a match with my MPX (latest Gen Competition model), with zero issues. I have been shooting American Eagle 115 almost exclusively through the MPX.

 

Sunday, I shot another match and part way through the first stage, I heard a funny report, but since the steel I was shooting fell over, I didn’t think it was a squib. When I went to engage the next array, the MPX wouldn’t cycle, and I had to manually chamber each successive cartridge to finish the stage. Since I was also registered for CO, I put the MPX aside, and waited to get home to figure it out. 
 

The BCG was fairly dry, so I lubed it, and then removed the hand guard to clean the gas system. When I looked, the gas plug was gone, and I assume that the noise I heard was when the plug exited the MPX.  It has been 800 rounds or so since I cleaned the gas system, so it is unlikely it was installed improperly. Has anyone observed this or heard of the gas plug coming off? 

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The only only time my gas plug fell out was when it wasn’t installed properly. I didn’t make sure it “clicked” into place when I rotated it during installation. 
 

Good thing it fell out when I was checking the zero since I just cleaned it. It fell out of the ejection port after I had shot about 15 rounds.

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Was the detent that holds the plug from turning still there? How many rounds on the rifle? Ever changed the rings on the plug? 

 

I have not heard of the wing (or whatever its called) that holds the plug in the piston housing to sheer/break off but I assume its possible? 

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Detent was still there, and it is the original part. No exact round count but likely under 2,000 rounds.

 

I guess it is possible I installed it improperly, but you would have thought  it wouldn’t have taken hundreds of rounds to dislodge. 

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4th time I have heard /seen this happen.. 1st was AZ state PCC match stage 10 guy on my squad plug never found, detent was sticky..2nd local match guy on my squad plug was found, detent was sticky... Last month a friend called while I was driving home from a match, Plug not found told him to check the detent and gave him info on a replacement plug..

 

My theroy is that if the detent is not latched in solid (or is sticky due to carbon fouling)  it starts to rotate due to vibration then the gas acts on the side of the slot to finish the rotation and eject it..  

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3 hours ago, Bdh821 said:

Geez maybe ill change mine out as it's one of the few parts I havent changed yet.

My maintenance issues went down 80% after Igot a big Ultrasonic tank the whole barrel will fit in (catty corner), this is the solution I use:

https://www.brownells.com/gun-cleaning-chemicals/solvents-degreasers/solvents/sonic-tonic-precision-ultrasonic-firearm-cleaning-concentrate-prod129724.aspx

 

Got a cheap  Tea Ball from Wallmart for the small parts...

 

Got to keep the expansion chamber in the gas plug free of carbon/lead build up, as it fills up you decrease the delay prior to the start of the unlock/ extraction process  

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  • 2 weeks later...
On 2/16/2021 at 12:48 PM, George16 said:

The only only time my gas plug fell out was when it wasn’t installed properly. I didn’t make sure it “clicked” into place when I rotated it during installation. 
 

Good thing it fell out when I was checking the zero since I just cleaned it. It fell out of the ejection port after I had shot about 15 rounds.

Remember last summer at SAPSA?  I installed the gas plug but never turned it into battery, wife had interrupted me!!

We had to put new gas rings on it- lost that stage- but not the match!!

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8 hours ago, Rolex said:

Remember last summer at SAPSA?  I installed the gas plug but never turned it into battery, wife had interrupted me!!

We had to put new gas rings on it- lost that stage- but not the match!!

Yup, that’s right.

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I guess you know,

 

But  just in case, if you need spare parts for you MPX, Rob (In Lead we trust) is the best source. I saw he is offering complete BCG as spare parts today morning. Don't know if he still has in stock.     

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+1 for ILWT.  I had my Gen2 gas port drilled out to 0.625, but to me that let too much gas through.  Even sub-minor brass was kicking WAY right.  I put in an ILWT 0.520 gas plug, and things are much more normal.  Rifle functions great after, and brass doesn't fly to the next zipcode. 

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