Has anybody increased the volume in their gas plug to reduce gas?  Either by removing washers from the original style gas plug or machining metal out of the newer 1-piece plug?  If so, how much volume did you add and how did it work?  

I’m looking mainly to make the gun cycle slower via reducing gas.

You're looking at this backwards.

I've got reduced size ports in my MPX's and the gas to the face isn't bad at all.

I don't think adding more gas into the system is going to reduce the gas that you're getting back in the face.  You're also going to speed up your bolt velocity, not slow it down my good man.

Try the ILWT reduced size ports.  I think you will like them.

On the contrary, everybody else is backwards!  Or I think you’re misunderstanding me.  

The gas port size is constant.  The gas plugs work by altering the volume of the chamber in front of the piston.  Larger volume means the same gas expands into more space which results is reducing the force/velocity of the piston.  Ie. “Reduced” gas from a larger volume.  

The ILWT gas plugs(they only make the adjustable plug now and it is too long for my purposes) all work by altering the volume of the chamber.  More volume = reduced gas action.  



This is a picture of two different gas plugs.   Note the volume difference.  


The original sig gas plug (gen1 and most(all?) of gen2) has washers which set the volume of the plug.  You can remove washers to get a larger volume(ie. Reduce the gas).  


Lastly, I’ll admit that I never knew the mpx vented gas from the gas system until I got one…. This makes gas tuning for minimum noise more important!
It also means gas tuning can have a much larger effect on gas face than if gas only came out the ejection port.  

Are these 2 plugs yours? Do you notice a difference between the 2 plugs in the same MPX? What model MPXs are the from? Thanks!

I found that picture on the internet while researching.  They are two of the original ILWT gas plugs(each plug a different gas setting).  ILWT quit making them and only make their adjustable gas plug.  I do not know which “setting” the plugs in the picture are.  

If you have the newer sig 1-piece gas plug you could reduce the gas with it by drilling metal out of the center of the plug to increase the volume,  I have no idea how much gas “setting” change results from a given volume change.  

I’m also curious if the 1-piece sig gas plugs are the same or different for various models of gen3 mpx.  Ie do the 16 inch and 4 inch mpx models use the same gas plug?

There are probably a couple of parameters that are getting mixed up in this discussion.  First, is the gas port diameter which essentially controls how quickly gas from the barrel enters the piston chamber.  This would control the speed at which the chamber pressurizes and pushes the piston which then pushes the carrier and unlocks the bolt.

Second, is the actual size, or volume, of the chamber.  This would delay the amount of time before the piston starts to move as the volume needs to fill with gas and pressurize before enough force is exerted on the piston face to move it.

Assuming there is always an excess amount of gas available, which is why the bleed-off port exists, then a simplified explanation would be the gas port size dictates the speed of the piston while the piston chamber volume would dictate the timing of piston movement.

It makes sense what the OP is saying, if we increase the piston chamber volume, it'll delay bolt unlocking and allow more gas to exit the muzzle rather than coming back down the barrel.

^^^ This doesn't appear to be correct. Their adjustable gas plug has separate ports of different sizes regulating the gas coming into the system.

From their site: Four adjustment positions;
0.) No Gas
1.) .0469
2.) .0520
3.) .0625
https://inleadwetrust.com/product/adjustable-gas-plug-for-mpx/

In this video, one can see the different ports on the end of the plug...
https://www.youtube.com/watch?v=kejPIPcS6Tk

Interesting, looks like the adjustable plug does have ports that overlap the barrel port.  
You can clearly see the old fixed adjustment plugs have no port and work by changing the volume.  

I’ve never seen or used the adjustable plug because it is too long for me.  I’m curious why it is made so long when it could easily be much shorter?

I think you’re confusing ILWT’s old non-adjustable plugs with Sig’s more recent “open” style gas plug. The pic you posted above of the 2 gas plugs are 2 versions of Sig’s open gas plug. IWLT’s discontinued non-adjustable plugs had a single port that overlapped the gas port regulating the gas coming in to the system. They were available with the 2 middle sizes from my previous post.

I don’t know why the ILWT adjustable is so long, maybe to making adjustments easier?? I don’t know why it’s in multiple parts either.

ILWT also sells replacement open style gas plugs similar to Sig (later gen, not sure which version). I suspect either could be used to be drilled larger for more volume as per your OP. Is this what you’re going to do?

Here’s links to 2 different factory plugs and both look newer (not gen 1 style). I called them a while back to ask the intention of the “high impulse” plug before they sold out, but they didn’t know the answer. I also called Sig, they didn’t know the answer and claimed they’d call me back, but they didn’t. I also asked the resident Sig expert here and didn’t get a reply.

Gas plug

High impulse gas plug

Sorry guys.  It's been a while since i've done anything with my MPX's.  I was only aware of ILWT's differing port size plugs as CJ mentioned.

ILWT made another batch of the fixed gas plug in the smallest size because enough people asked for it….  I got one and it does indeed have a small hole that overlaps the barrel port.  I think I was the victim of some classic interweb misinformation!  

I’m using it on a spare sig barrel that is shortened, so I also have a spare sig gas plug with the stack of washers. I’m going to try changing the assembly of the sig gas plug also to see if it can help with noise.  

Since this thread started I also tried geisselle recoil springs - the weakest of the three worked great on a stock sig 8 inch barrel.  It shot even smoother and seemed a bit quieter(but hard to tell, could be the placebo effect).  

I’ll trying various combinations of the stiffer springs and ilwt gas plug this weekend.  Will also try a modified sig gas plug.  

Now that I’ve got a spare barrel I’m considering building an integral silencer with ported barrel to keep ball ammo subsonic like an mp5sd.  Anybody done that?  

Thanks for that ^^^ I just ordered a fixed small port plug. I’m running a MPX-K with a direct thread Omega 9k that I leave on. I also tried the Geissele springs and found only the lightest would work reliably. I’m hoping this plug will make them unreliable, so I can go back to the stock springs, as I think the springs are a bandaid solution for excessive gas.

Same here.  The weakest G spring works great, the middle one doesn’t hold the bolt open with subsonic ammo unless a silencer is on.  The strongest is too stiff.  

All the springs are so stiff it feels like the flimsy charging handle will break eventually!  I’m also hoping the gas plug will be the answer.  By my numbers the small ilwt port is 73% of the area of the barrel port so I’ve got my fingers crossed.  Hope to have time to test it today.  

I think sig did it wrong by having the port so close to the chamber, if it was even just an inch down the barrel it would be so much better.  

ETA: with the ilwt fixed small plug, sig springs, and my 5ish inch barrel it sounded quieter inside than it did outside with the 8 inch barrel and stock gas plug.  The ilwt plug is definitely the ticket if you want quiet.  I didn’t get to try it with the G springs and probably won’t - I don’t like how stiff they are.

I’ve never tried it without the suppressor, but in my case the middle spring wouldn’t reliably lock back on empty.

My plug arrived yesterday, installed it last night, and shot it today. I wish I could have done a side by side or before and after comparison, but unfortunately that’s not possible, at least not for me with one MPX at the local range. With the .0469 gas plug mine still functions fine and locks back using the +30% Geissele red springs even though I was hoping it would be so restrictive that I could go back to the stock springs. Oh well.

I intentionally redirected the ventilation to see how gassy it would be worst case and it was quite gassy and coming out of the piston area, the bottom of the magwell, and ejection port. With the ventilation adjusted correctly, it was fine. I’m not complaining about the gas either, just trying to reduce it with some mods.

One thought about possibly easily reducing ejection port gas: I recall Marvin Pitts suggesting to buyers of his ACR gas system, if they experienced excessive bolt speed as a result of a too large gas port on their donor AR barrel, they could remove the piston rings. Doing so makes it less efficient due to gas blowing past the piston. On the MPX this efficiency could be reduced at the piston as well as the plug. I realize more gas would leak the piston area, but I wonder if it would reduce the bolt speed and reduce a larger about of gas at the ejection port?

ETA: I’m not suggesting one remove the piston rings without careful evaluation, but perhaps switching to less efficient multi piece rings instead of the single piece ring, or removing the stationary plug ring which would be preferable over the moving piston ring, or putting in well used rings, etc.

If you remove the rings I’d be worried about scoring the piston or gas block.  

The problem is the port is so close to the chamber, if it was just an inch or two down the barrel it’d probably be better.  
I wonder if the in lead we trust guy could make A barrel and gas block with the port moved an inch or two down the barrel.  Would slow the bolt opening and reduce gas flow significantly….