Tight Fit in Grip Module and Trigger Reset Issue

SNBI125

SNBI125

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Hello. I currently have 3 completed MUP-1s as well as a factory FCU from my first P320. While finishing the MUP-1s, I was having issues with trigger resets and what seemed to be the FCU not really moving freely within the grip module when I would pull the trigger with no slide attached. As far as the trigger reset, it was only an issue if I held the trigger down after firing (or dry firing). If I keep it pressed, I have to nudge the trigger forward a bit to reset; if I don't, then it resets on its own.
Anyway, I swapped some parts around and they all seemed to be working. Now, I recently picked up a Mirzon grip module, and it seems to maybe be a little tighter than the Sig grip modules I've had, and I'm basically having this same issue with that. It seems to be with all 3 MUP-1s, but not with my factory FCU. I've had it at the range with one of the MUP-1s. It fired fine but just had to nudge the trigger forward to reset if I kept it pressed while firing. With the slide removed, it just feels really tight when I squeeze the trigger, like it's clogged with molasses or something. This is not a problem with my factory FCU in the Mirzon, or with this same MUP-1 in my Sig grip module.
Anyone know if this is a common issue with the either the Mirzon, or do my MUP-1s need a little more work?
 
Bumping this thread as I've just finished another P320 build and having a similar issue. I had fixed the issue with the Mirzon grip by polishing the inside of the grip just a bit and smoothing things out, now everything moves a little more freely and the trigger resets consistently.

The build I just put together is another MUP-1 with a VTAC slide I picked up slightly used, and a new Sig X-Carry LXG grip module, plus the grip weight. Basically the factory VTAC configuration, plus the upgrades to the grip module. I got it to the range yesterday and had to nudge the trigger forward a tiny bit to get it to reset after every shot.

I also don't know whether this is related but I've noticed that my MUP-1s do not stay together like my factory FCU does. If I don't hold it together carefully, it falls apart (when it's outside of the grip module, I mean). And not entirely - mainly the trigger and 1 or 2 of the pins toward the front will fall out.
 
Bcichlid said:
i recall p80 ralph had similar issue with the trigger watch his vid


View: https://odysee.com/@p80ralph:0/80-jsd-supply-mup-sig-sauer-p320-x5:a
Click to expand...

Thanks... I do have some parts I can swap in, didn't really want to install a new aftermarket trigger to solve this issue. But I'll take it apart and see if anything helps. This grip module isn't nearly as tight of a fit as the Mirzon. I'd read that about the Mirzon grips so it made more sense that that was needed. It was difficult to install the FCU at all. Not so much with this grip module, but still the issue with the trigger. We'll see.
 
In the video at min 5:20 he points to the area that need to be examined, mentions that he put some lubrication on the slide as well at the contact point. Watch that part over before replacing the trigger.
I dont have any experience with sig build, im sure some other members here can give their output on your problem as well.
here some info from sig forum
www.sigtalk.com

P320 M17 Trigger Reset Problems

www.sigtalk.com www.sigtalk.com

 
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Thanks, those are definitely going to be helpful since I currently have 4 MUP-1s that all seem to have at least some little bug to work out. I had already swapped the trigger bars (and maybe the triggers, but not sure whether I mixed them up) between this one and my one factory FCU. Now both seem to be working, at least with dry firing. One thing I've noticed with these MUP-1s (the three I've currently drilled out and assembled) is that the trigger bars never seem to fit quite the same way as they do on the factory FCU. The ones on the MUP-1s always seem to stick out a tiny bit to the right and the pin in the trigger wasn't quite centered, even though it would still move the trigger bar. But, it did fall apart easily like I mentioned. But now both of these look right and fit more tightly, so maybe I was putting it together wrong.

Hopefully I'll get these back to the range this weekend to make sure both function right with live fire.
 
Ok so I watched the SigGuy video about FCU re-assembly and I think I know what might have been part of my problem. I think that instead of resting the back of the trigger bar behind the sear housing, then lining up the trigger pin and the hole in the trigger bar, then moving the trigger bar into place in front of the sear housing, what I was doing was just putting the trigger bar in place in front of the sear housing, then installing the trigger. It would work, but wasn't a tight fit. It fell apart easily outside of the grip module.

However, even though I was able to put it together properly with my factory FCU (with the swapped trigger bar from my first MUP-1), and my first MUP-1 (and the factor FCU trigger bar), for the life of me, with my second MUP-1 (with parts kit trigger bar) I could not get the trigger pin lined up with the hole in the trigger bar, with the back of the trigger bar still behind the sear housing. I don't know if there's a trick to this that I'm missing, or if this one is just being really difficult. But it definitely made a difference with the other two, both were a tight fit and not falling apart, and everything functioned correctly (trigger reset, etc.) while dry firing.
 
I found a few things in some other Sig Guy videos that helped to some degree.

1) The trigger spring can get misshapen with repeated assembly/disassembly. So I tried a spare one and while I still couldn't get the trigger and triggerbar to meet, it did make a difference once I put the FCU back in the grip module. It was resetting like it should. I tossed that old spring and plan to pick up a few spares.

2) The flat/X-series trigger has a slightly different shape on the back side that makes it more difficult to pivot rearward to meet the triggerbar. I took out the one curved trigger I still have and was able to do the installation much more easily with that one. There was still a bit of a gap between the triggerbar and the FCU frame but it functions correctly. I'll give it another try in another one and see what happens. Doesn't really help with my other triggers (all the flat style) but at least with lower expectations, it isn't as frustrating.
 
I dont have any experience with SIG builds, last time i checked it was around 1K per build
in total cost of all the pars and jig.
Is that still the case today?
My head is always get spinning when looking at the internal parts of that MUP and its pats
good job SNBI125 of getting them to function malfunction free.
 
last time i checked it was around 1K per build
Click to expand...
My experience is about in that ballpark. magazines are a lot more expensive too.

As with all the platforms, I would say unless you know you will do multiple builds, just get what you need as an FFL item. It will save you money on jigs, tools, etc.

Example - this gets you going very economically:
SIG P320 OEM FIRE CONTROL UNIT WITH LOWER PARTS KIT - FFL ITEM
 
Well, there's a wide price range with Sigs in general, whether you build or buy retail. You can get a brand new, fully assembled, serialized and warrantied FCU for about $350 - $400. You can actually build the MUP-1 for about the same or even a little less, depending on how many you spread the cost of the jig across.

So yeah, building these to save money would not make any sense. But if you like building and/or owning items that you know have never been in any government database, the difference in cost isn't substantial. When I look at the price of new Glocks, I'm pretty sure they're way less than what I put into comparable P80 builds.

If you wanted, I think you could build a lower-end P320 for around $700-800, but if you know you won't be able to resist all the other cool options, $1K+ is more realistic. You're going to want to do more than one to spread out the cost of the jig, and you're certainly not going to want a bunch of the same bare-bones builds.

Also, aside from the trigger issues I'm dealing with, all those tiny parts aren't as scary as they look. The more tricky part is getting the rails done right. It's easy to think you have them hammered out and sawed off properly, only to have to do more work when you can't get the slide on.
 

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