New MPX. Cycle issues

[MrRick]

So took my brand new MPX to the range today and as I read in various places, use factory ammo before trying low PF ammo. So I started with  a 100 WWB ammo and it ran 100%. The issues started when I went to use Federal Independance ammo. First few rounds no problem then it started to short stroke. I thought maybe it was the ammo, so I used another type of ammo I had (reman) but it was worst. I lubed the rifle with the supplied Lucas oil and still same issue. So I went back to the Federal and it was pretty much a single shot rifle. Went and got some Hornady Critical Defense +P ammo and same thing so I wrapped it up from there. Rifle was cleaned and lube with CLP before going to the range. Any ideas what to looks for?

[Mulligan03]

From what i have got from other mpx shooters on here the manufacturered 9mm is a little to long to run great in mpx.. OAL needs to be 1.12.. going to try this myself since i am having the same issues with my mpx .. have precision delta 124s coming in tomorrow.. gonna try and get some loaded and see what happens.. will post results on here

[MrRick]

Update:

Took a look at it now and found the cap on the gas valve loose and easy to rotate with my thumb. Screwed it all the way in but if I'm understanding what I'm reading, there should be a roll pin holding it in place?

[Neomet]

Photo??

 

[MrRick]

Did a bit of research and there's supposed to be a pin holding it in place. Mine is missing. So I installed a pin with the cap where it should be. Will see tomorrow how it goes. Not my actual picture but the cap I'm talking about. 

[ctay]

I don't have any pin in the gas plug on either of my MPX's. Just make sure it is twisted all the way over and it should be good to go. 

[MrRick]

I'm talking about the cap itself. The one with the 3 holes in front. If you remove it a rod with like 20 tiny spacer comes out. 

[MrRick]

So here is the cap. This is what it looked like after the first range trip. 

 

Apparently there is is a pin that is supposed to hold it in place. 

 

 

So I installed it and put a pin through it. Took to the range and still doesn't cycle. I think it even got worst. Before it would cycle enough to reset the trigger. Now it doesn't do that. 

[Aircooled6racer]

Hello: I would give Sig a call and get a call tag to send it back. Thanks, Eric

[MrRick]

So I took the pin I made out and screwed the cap all the way in.  Now I can get it to run all the ammo I put through it (didn't try my 147 ammo) and it ran fine as long as I kept the cap tight (kept coming loose). So now to figure out how to keep the cap in place. 

[MrRick]

So I finally figured out the whole issue. So when my plug came out the first time, so did the spacers. I though they were just simple spacers. Found the order they are supposed to sit and this puts the cap in the right location to put the pin in the correct spot. With this done, I manage to get the gun to run pretty much anything. Was finally able to run mag after mag to the point I got tired of shooting it (about 350 rounds may be 400). Now I need a red dot since mine went out (Holosun). 

Edited February 6, 2017 by MrRick

[pitvpr]

Be aware,

The roll pin that holds that cap in place is "walking" out on mine, I have to press it back in every 500+ rounds or so. That cap needs to be screwed all the way for the gun to cycle properly.

 

Contacted Sig, they claim the roll pin may be damaged or worn, they are sending me a couple of new ones. I would have a couple of these pins in on hand and recommend checking this at every cleaning...

Edited November 21, 2017 by pitvpr

[MrRick]

I contacted Sig, and they sent me a whole new valve. So I had a spare. 

[SergioSF]

My roll pin is still there - I’ve never taken it out. 

But it looks like it the cap has backed out a little bit, exposing a thread or two. Is that normal or should it be flush? 

Edited November 21, 2017 by SergioSF
clarity

[MrRick]

That’s normal. 

[SergioSF]

Just now, MrRick said:

That’s normal. 

 

Thanks!

 

[pitvpr]

I think the cap will be able to rotate somewhat, but no more than where yours is. I think your okay as long as the pin doesn't come out and allow the plug to unscrew as much as the the picture from MrRick...

[MrRick]

Mine looks like Sergio posted now. 

[SergioSF]

My MPX, after shortening the barrel to 5.125" is no longer reliably running my barely-making-powerfactor 147s, despite having the gas port opened up to .0625.

It ran it just fine before, with the full 16" barrel and .060 port. 

 

I saw MrRick's pic and thought maybe mine had the same issue. 

 

 

[pitvpr]

On 2/3/2017 at 9:18 PM, MrRick said:

 

 

After taking another look, my cap is all the way in FLUSH, like this picture...haven't had any issues

 

[SergioSF]

52 minutes ago, MrRick said:

Mine looks like Sergio posted now. 

 

Yours doesn't screw all the way flush?

[MrRick]

1 hour ago, SergioSF said:

 

Yours doesn't screw all the way flush?

Nope. It shoot fine though. My original valve, I screwed it all the way in and made a pin to lock it in place. Both valves work. 

[SergioSF]

25 minutes ago, MrRick said:

Nope. It shoot fine though. My original valve, I screwed it all the way in and made a pin to lock it in place. Both valves work. 

 

Good to hear. Thanks!