Opening Mpx gas port

[Dirty_J]

Just got a Gen2 mpx carbine that runs like a champ with hot-ish ammo (Blazer/Speer 124's), but short strokes like a mo-fo with my AR9 PCC load (135 blue bullet over 3.4gr sport pistol). That load yields about 140pf in the 16" Ar9. It was basically a single shot with this ammo. 

 

Also tried some 150gr Federal Syntech. Was slightly better than my loads, but still couldn't go more than 2-3 rounds before a short stroke/double feed. 

 

Really not interested in running factory ammo. So either the ammo really just isn't hot enough or it just doesn't dig the burn rate of the powder. 

 

I know Sig choked down the port size on the Gen2's. Looking to open the port to run my loaded ammo. 

 

I'm mechanically inclined, can certainly take it apart and put it in the drill press. 

 

Any challenges that might not be obvious at first glance?

 

- remove barrel/gas assembly 

- drive out barrel pins

- pull barrel from gas valve 

- drill barrel and gas valve to new size 

- reassemble

 

 

[Gregg K]

I would run a few thousand through it before making any changes. My gen II runs fine on 93 PF loads. I would take everything apart including the gas system and give it a good scrubbing out and try again. I run a medium powder, BE-86

[Underwood]

6 hours ago, Gregg K said:

I would run a few thousand through it before making any changes. My gen II runs fine on 93 PF loads. I would take everything apart including the gas system and give it a good scrubbing out and try again. I run a medium powder, BE-86

I agree with this.. I have over 8k rounds threw mine and the gas system and springs are all factory. Give it a good detailed cleaning. I remove and clean the gas system after every match.

Mine runs anything i feed it, even 95 grain hollow points with 3.2 tightgroup.

I don't hand load anything further than 1.150

 

Edited January 3, 2019 by Underwood

[GregJ]

Ditto to above.  Run a few thou of OEM ammo through it to break it in, then start messing with stuff.  If you still need to open the gas port, Rob Otte at https://www.inleadwetrust.com is the go-to guy for MPX issues.

 

My Gen 2 has run great since I've had it (bought it used).  I run my same loads I shoot in my CO pistol, which makes about 140PF in my MPX carbine.  124 gr Zero, 1.100, 4.1gr W231. They do need a little gas to run. 

 

Another word of caution, do not lube the piston rings and tappet rings.  Keep the piston system free of lube.  All else, the MPX likes to be very wet. 

Edited January 3, 2019 by GregJ

[Dirty_J]

53 minutes ago, GregJ said:

Ditto to above.  Run a few thou of OEM ammo through it to break it in, then start messing with stuff.  If you still need to open the gas port, Rob Otte at https://www.inleadwetrust.com is the go-to guy for MPX issues.

 

My Gen 2 has run great since I've had it (bought it used).  I run my same loads I shoot in my CO pistol, which makes about 140PF in my MPX carbine.  124 gr Zero, 1.100, 4.1gr W231. They do need a little gas to run. 

 

Another word of caution, do not lube the piston rings and tappet rings.  Keep the piston system free of lube.  All else, the MPX likes to be very wet. 

Yeah. I've already talked with Rob. He called me on New year's day actually. Great customer service. 

 

I'll for sure be buying spares from him. 

[Dirty_J]

He actually recommended opening the port. Is sending me an opened gas system/barrel to try first to see how it works with my ammo

[Aircooled6racer]

Hello: Shoot 115 grain bullets at 138-145PF and your MPX will run great. Lube it very well, like very wet and it will run. I have had 3 MPX's all gen 2's and they all ran great with the stock port diameter. Currently running a tuning fork barrel on one of them and it runs great also. I can't stand the tuning fork sound so it will be getting a mod soon. The MPX is not like a AR9mm so don't load it like one. Thanks,  Eric

[Dirty_J]

5 minutes ago, Aircooled6racer said:

Hello: Shoot 115 grain bullets at 138-145PF and your MPX will run great. Lube it very well, like very wet and it will run. I have had 3 MPX's all gen 2's and they all ran great with the stock port diameter. Currently running a tuning fork barrel on one of them and it runs great also. I can't stand the tuning fork sound so it will be getting a mod soon. The MPX is not like a AR9mm so don't load it like one. Thanks,  Eric

My load is what I run for production and PCC. What exactly do you mean by "don't load it like an AR9"? 

 

132 PF in a CZ Shadow 2 and 144 PF in a 16" AR9. 

 

Even with the shorter pinned Mpx barrel, i can't imagine the load is less than 138PF. (Though I have not put it on the chrono yet)

 

So unless the gun is quite picky of the burn rate with a 135gr projectile... I would think it should be adequate. 

 

 

[Aircooled6racer]

Hello: Load it with lighter bullets than your Production pistol uses. AR9 loads are usually in the 131-134PF which means in a MPX it is around 115-120PF. I would load for your Production pistol and load separate loads for your PCC's. Custom loads will work better. You have to keep track of the different loads but using different bullets or primers helps with that. Silver primers for pistol loads with coated bullets and plated bullets with brass primers is just one way. I load JHP 115's for open, 124's for AR9, 135's/147's for Production, RN 115's for MPX. One load for everything is not that great is all that I am saying. Thanks, Eric

[Dirty_J]

Just now, Aircooled6racer said:

Hello: Load it with lighter bullets than your Production pistol uses. AR9 loads are usually in the 131-134PF which means in a MPX it is around 115-120PF. I would load for your Production pistol and load separate loads for your PCC's. Custom loads will work better. You have to keep track of the different loads but using different bullets or primers helps with that. Silver primers for pistol loads with coated bullets and plated bullets with brass primers is just one way. I load JHP 115's for open, 124's for AR9, 135's/147's for Production, RN 115's for MPX. One load for everything is not that great is all that I am saying. Thanks, Eric

The 135gr load works great in the AR9 actually. I worked up several dozen different projectile/powders to find a Goldilocks combo... a shame the MPX can't also play nice with it 

 

The Taccom 3 stage buffer has the AR9 shooting wonderfully with my preferred load. Feels much softer than the number coming off the chrono. 

 

[TRUBL]

I guess I really do not understand......when reloading, or at least the way i was taught. You reload for the weapon and not make the weapon for the reload. AND.....in the case of the MPX, there is absolutely zero reason to shoot a bunny fart load in that system......well, unless you want the gun NOT TO CYCLE. All the top guys that run the MPX are NOT running light loads......they are running loads at near factory specs. Ya know why? 1) the system was designed for that and 2) the system with near factory or at factory specs recoils WAY less than any comparable AR9 that is blow back. 

[George16]

9 hours ago, Dirty_J said:

My load is what I run for production and PCC. What exactly do you mean by "don't load it like an AR9"? 

 

132 PF in a CZ Shadow 2 and 144 PF in a 16" AR9. 

 

Even with the shorter pinned Mpx barrel, i can't imagine the load is less than 138PF. (Though I have not put it on the chrono yet)

 

So unless the gun is quite picky of the burn rate with a 135gr projectile... I would think it should be adequate. 

 

 

 

I have a two month old 8” barelled MPX and so far no problems running my bunny fart loads for my Shadow 2. The loads chrono’s around 126 PF on the Shadow 2 and around 135-138 PF on the 8” MPX. 

 

All I did after I picked it up from the LGS was clean and lube it well then shot about 200 rounds of factory federal ammo. After that, I had been using my Shadow 2 reloads which is 124 Gr PD JHP with 4.1 Gr Winchester  231@1.125- 1.128” OAL.

 

Shot my first PCC Match two weeks ago and ran great. No malfunctions of any kind. All the springs are factory with the exception of the recoil pad. I bought and installed a Taccom wave spring recoil pad and its running great.

 

Now, I only need a Taccom mag splice and I’ll be set.  I wish it comes back in stock again.

 

 

Edited January 4, 2019 by George16
Need instead of “did”

[2011BLDR]

if you ever plan on putting a comp on an MPX I WOULDN'T recommend opening the gas port.

[Acer2428]

I have a Gen 1 (Actually two of them), so opened up gas port vs. the Gen 2. 

 

I run a 124 JHP over 3.5gr of Clays (Yes, just clays) So super fast burn rate. Works just fine. I tried power pistol since I had it and it has a slower burn rate, but the recoil/flash was much harsher. Basically, open it up, don't know why that wouldn't work. I run the ILWT +20% springs and still have no issues with cycling. I do not have LRBHO with that load though. Zero hiccups so far. 

 

So sure, you could load for it, but IMO, open it up.

 

I also run a Lantac Comp, zero issues. Not sure what @2011BLDR is getting at. Care to explain?

Edited January 3, 2019 by Acer2428

[Dirty_J]

Ya... I don't really follow how a comp would affect blowback gasses... would be marginal if any impact 

[2011BLDR]

1 hour ago, Dirty_J said:

Ya... I don't really follow how a comp would affect blowback gasses... would be marginal if any impact 

 an MPX is NOT blowback... 

on my 2 MPX's ..to see maximum effect I have needed to play around with:

• load and / or factory ammo choice
• Gas port size ( gen 2 guns seem to be out their with either 0.0520" or 0.0625" so far no idea yet on the "competition"  )
• Gas plug size

The MBX  comp can build  back presser ( resulting in over gased at the piston)  with the right loads or reduce port presser with other loads ( resulting in under  gased at the piston )  all depending on powder burn rate + peak presser due to the 13.2" of dwell time in the barrel  .. lots of room to play... but I only have 35,000 rounds on my 2 MPX's 

[Dirty_J]

Ya. I understand it's not a direct blowback. 

[DavidSeavey]

my gen2 would short stoke my 147/3.2 titegroup minor pistol load early on so i just used factory ammo until i developed my current load of a 115 over about 5 grains of WSF, a slower powder than the WST and titegroup i had tried early on, and cleaner than hs6 at that load weight.  i didnt want to open my port up just so it'll run any factory ammo similarly soft should i travel for a match and need additional ammo, plus it's already quite soft shooting to begin with.

 

i am curious now though, next time i bring it out i'll have to try it with my 147 titegroup load now that she's seen thousands of rounds and see if she plays well.

[NinerRider]

12 hours ago, Dirty_J said:

He actually recommended opening the port. Is sending me an opened gas system/barrel to try first to see how it works with my ammo

 

Rob is a great guy and I would follow any advice he gives. I have opened up the gas ports on all three of my Sig mpx's. If you are only doing one gun then send it to Rob to do, you can't buy the carbide bit and armory block for what Rob will do it for. As for loads I ran 147 extreme with 3.6 gr of CFE for a solid year with no problems before I opened the gas port.  You want a slower burning powder to create more gas fast burning powders like titegroup will not cycle reliably at low pf.

 

[2011BLDR]

I had one barrel port opened and I do reget it ... I have to run the most restricted gas plug on that barrel.. if you not going to put a comp on and try to drive it then YMWV...

[Dirty_J]

19 hours ago, 2011BLDR said:

I had one barrel port opened and I do reget it ... I have to run the most restricted gas plug on that barrel.. if you not going to put a comp on and try to drive it then YMWV...

What ammo are you shooting ?

 

What's the sysptom caused that forces you to run the restricted plug?

[Dirty_J]

Two day turn. Opened  gas port barrel to try. Now that's SERVICE. 

 

Hitting the range tomorrow. We'll see how it runs. 

[2011BLDR]

25 minutes ago, Dirty_J said:

What ammo are you shooting ?

 

What's the sysptom caused that forces you to run the restricted plug?

Speer 115 or 124 gr TMJ or hand loads that are equal in velocity per bullet weight... your stated goal is to have a MPX that runs your production and AR9 load..

My goal is:

•  have my MPX's run the same cycle time as an open pistol or an AR so that I don't have different timing
• Have minimal movement in the sight
• Have a 19"  drop @ in the 150 -180  yard range we shoot dedicated PCC matches that place targets out that far

[Dirty_J]

Oh. Ok then. 

[TDH]

On 1/3/2019 at 8:31 PM, DavidSeavey said:

my gen2 would short stoke my 147/3.2 titegroup minor pistol load early on so i just used factory ammo until i developed my current load of a 115 over about 5 grains of WSF, a slower powder than the WST and titegroup i had tried early on, and cleaner than hs6 at that load weight.  i didnt want to open my port up just so it'll run any factory ammo similarly soft should i travel for a match and need additional ammo, plus it's already quite soft shooting to begin with.

 

i am curious now though, next time i bring it out i'll have to try it with my 147 titegroup load now that she's seen thousands of rounds and see if she plays well.

 

I had a similar experience with my gen2 except I switched to 125 RN and some CFE Pistol I had laying around. After 2k rounds, I tried my 147/TG load and it ran 4 mags without issue. But at this point, I'm happy staying to the cheaper bullet with slower powder that is better suited for this operating system. I'm glad I didn't messing with opening up the gas port.