Seeking Help / Recommendations for MWS GBBR Full Auto Gas Leak & Tech Repair UK

[SullivanTrEE]

Hi all, I’m having a persistent issue with my Guns Modify TM MWS GBBR — in full auto it leaks gas like crazy (almost “spraying out” from the nozzle area). I’ve contacted Guns Modify support already and they kindly sent me upgraded parts, which I installed into the nozzle and trigger box, and it did help for a while… but now the leaking/over-venting has come back.


I’ve tried everything I can think of at this point and am stuck. Does anyone have experience with this specific issue (full auto blow-off / gas venting)? Could it be a nozzle seal / NPAS issue / trigger timing / hammer/valve set problem? (I’m also open to parts advice.)


Additionally, I’m looking for a tech / workshop that can do MWS GBBR repair & diagnosis — preferably someone familiar with MWS systems.
Any recommendations, contact info, or personal experience is greatly appreciated!


Thanks in advance!

 

[woody_2231]

what mags are you using? Newer GM pmags have gas through put problems, and is more temperature sensitive than Stanag mags.

 

[SullivanTrEE]

what mags are you using? Newer GM pmags have gas through put problems, and is more temperature sensitive than Stanag mags.

Click to shrink...

I’m running Guns Modify PMAG V3s and also Angry Gun Lancer mags.
Sounds like I probably should grab a couple of Tokyo Marui STANAGs and test for comparison — especially if the newer GM PMAGs are more sensitive to gas throughput and temperature.


Thanks for the heads-up

 

[Ronin0033]

I’d have a look at changing your Hop rubber if this is still an issue. Hop rubbers can sometimes expand if they get oily, trying a new rubber can at least rule that out.

Out of interest what parts did GM send to fix the issue?

 

[SullivanTrEE]

I’d have a look at changing your Hop rubber if this is still an issue. Hop rubbers can sometimes expand if they get oily, trying a new rubber can at least rule that out.

Out of interest what parts did GM send to fix the issue?

Click to shrink...

My hop rubber and inner barrel were both replaced very recently, and I haven’t even fielded it since the change. So I think we can safely rule that out.


Coincidentally, Guns Modify just released a new nozzle set. I’m planning to get the adjustable version, which should also help me rule out the possibility that the NPAS I installed is causing the issue.


GM sent me a new roller and reinforcement block for the bolt. Here’s the installation guide in case it helps:
https://www.gunsmodify.com/Page7?article_id=418

 

[n00b1982]

Personally,

I have always found the the GM PMag - regardless of version - is particularly poor for full auto use and have come to accept that they are to all intents and purposes only for semi auto.

The only other reason that I have found for gas venting is overfilling the mags. Not sure of your own experience level so not trying to teach you to suck eggs, but a surefire way to tell if you are over gassing is to actually weigh the mag with around 10 seconds of gas. This is more than enough to empty a mag out from full as well.

Ultimately it’s because of problems with other magazines that many just go back to the TM Stanags - you can’t overfill them, and they just work with the gun however you use them as intended.

A lot of people keep 1 GM for pics as they look cool, but after two years of use and having to reseal them at least three times each on top of their other quirks they are not a great mag for general use.

As a side note, been using the MWS platform for about 9 years ish and been through many different variations of internals, mags etc. The only other potential thing is when you had the parts upgraded did you have a 4UAD bucking installed? These can sometimes cause issues with over sealing which can lead to similar issues too.

Hopefully there’s something there that will help, or give something to think about.