Sig MPX PCC

[smoker 01]

Hello I recently got myself a Sig MPX PCC

I do reloading at 130 to 135 power factor

Does sombody know why I do not get the 30rounds magazines running (I got 2)

The 20 rounds magazine are no problem at all they run all day smoothly without any problems....

All magazines are the new models so 2e generation

I really do not understand why the big ones are not running without any problems

If I take standard 9mm factory they will run oke but why not with reloaded ammo , the 20 rounds stick runs without any problems at all

I also made ammo with the same factor as factory ammo but they also do not run decent

Reloaded ammo is loaded perfect one time fired brass (they run in the 20 rounds stick perfect so ???)

I hope someone can help me I really like the Sig and certainly the recoil wich is making me very happy

[inertia]

So what is happening is the 20 has an aggressive limiter in it that provides different spring tension than the 30s. Your current reloads do not produce enough gas to cycle that gun with those mags under current conditions. Note I said gas not PF, this is a gas gun not recoil operated so the function envelope is determined by gas not pf. Here are your options: 1. Develop a load that generates more gas, this is most easily accomplished by using more powder, you dont need more pf so you should use a lighter bullet or slower burning powder,  both necessitate more powder for same PF. 2. Reduce spring tension by breaking in the mags springs, adding extensions or some combination. 3. Break in the gun and mags, depending on age lubing it up, using the mags a lot and shooting that sucker can loosen things up and resolve the problem.

Edited January 7, 2020 by inertia

[Neomet]

Quick and dirty way to tell if your ammo has enough "kick" to it.  Put a single  round in your biggest mag.  If the bolt does not lock back you need to increase your powder charge.  Don't worry about your PF going up.  Unlike blowback guns you will hardly notice any difference between 130 and 150PF in the MPX.  
 

[ck1]

28 minutes ago, Neomet said:

 Unlike blowback guns you will hardly notice any difference between 130 and 150PF in the MPX.  
 

Word. The MPX at around 145ish+ power factor still feels softer than 125-130pf stuff in a blowback gun... actually was shooting with a buddy who runs a JP SCS setup tuned in pretty good with his 130pf loads and we were both amazed a little on how much softer the MPX seems against my 145-150pf factory stuff.

 

As an aside, I’ve been running the Syntech PCC-specific 130gr stuff at matches, but I got a hold of a case of S&B 124gr factory stuff that shoots almost identically, and at $0.15 vs $0.20 per round I think the S&B 124’s might just be my new go-to.

[Chillywig]

7 hours ago, smoker 01 said:

 

I do reloading at 130 to 135 power factor

 

Is 130 to 135PF out of the MPX? 16" barrel? What weight bullet? I would guess you would be sub minor out of a pistol with that load. Need more power, gas, energy, something

[inertia]

1 hour ago, Chillywig said:

Is 130 to 135PF out of the MPX? 16" barrel? What weight bullet? I would guess you would be sub minor out of a pistol with that load. Need more power, gas, energy, something

Good point, 130ish in my pistol = 135ish in my 8" mpx = 140ish I'm my 16" mpx, but he said he had issues with factory ammo and reloads ran in the 20 rounders. A new mpx with new 30rd  mags goes tend to just be really tight until it's all settled in.

[smoker 01]

Thanks for the response my Sig is the new model MPX PCC with 16" barrel

My load is Vitavuori N350 (slow burning powder) and I put 5 grains in there with a 124 bullit and I also loaded 115 with the same load , with the 124 was PF 146 and the 115 was 133PF

All and everything is working fine in the 20 rounds magazine (I loaded to 126PF and this magazine still works with no problem at all)  but not in the 30 rounds magazine that's what I do not understand

I really like this load so....(115grains with 133PF is great)

And also with this load the bolt does lock back (with all loads I made the bolt does lock back so I think this should be oke)

I do not know how a blowback rifle shoots but I do know there 's a difference between shooting PF 133 or 146 the 133PF is much faster on targets

The 30rounds magazine ONLY works fine with factory ammo ??? (factory ammo is 124 Geco and was 146PF)

I quess that load the 30 round magazine up with 30rounds and let it lay down for a few days maybe that helps

And yes the Sig is brand new only had 600 to 700 round true the rifle now

Is it true that 145ish+ power factor still feels softer than 125-130pf stuff in a blowback gun

Thanks again for response and I hope answers keep coming because when the MPX runs it runs great and would hate it to sell it

Gr

[ck1]

13 hours ago, smoker 01 said:

 

Is it true that 145ish+ power factor still feels softer than 125-130pf stuff in a blowback gun

I definitely think so. The two different recoil impulses are radically different back to back: blowback guns are more like a violent “thud/bang” when the action cycles, whereas the MPX cycles more like a fast “sling-shot/poof” type of feel... It’s hard to describe, but you can feel it when you shoot them back to back. You can tune a blowback gun with buffer system stuff and by short-stroking it to be close, but the stock MPX system is pretty much almost always softer and with less dot movement even when shooting higher PF ammo.

i should let it be known that I don’t really like Sig very much, and really wish the MPX system wasn’t proprietary, because IMHO, having to deal with Sig if one has issues is probably the biggest con going the MPX route.

Edited January 9, 2020 by ck1

[inertia]

15 hours ago, smoker 01 said:

Thanks for the response my Sig is the new model MPX PCC with 16" barrel

My load is Vitavuori N350 (slow burning powder) and I put 5 grains in there with a 124 bullit and I also loaded 115 with the same load , with the 124 was PF 146 and the 115 was 133PF

All and everything is working fine in the 20 rounds magazine (I loaded to 126PF and this magazine still works with no problem at all)  but not in the 30 rounds magazine that's what I do not understand

I really like this load so....(115grains with 133PF is great)

And also with this load the bolt does lock back (with all loads I made the bolt does lock back so I think this should be oke)

I do not know how a blowback rifle shoots but I do know there 's a difference between shooting PF 133 or 146 the 133PF is much faster on targets

The 30rounds magazine ONLY works fine with factory ammo ??? (factory ammo is 124 Geco and was 146PF)

I quess that load the 30 round magazine up with 30rounds and let it lay down for a few days maybe that helps

And yes the Sig is brand new only had 600 to 700 round true the rifle now

Is it true that 145ish+ power factor still feels softer than 125-130pf stuff in a blowback gun

Thanks again for response and I hope answers keep coming because when the MPX runs it runs great and would hate it to sell it

Gr

It's the springs in the 30 mags load them up try to cram 31 in leave them loaded or add extensions to loosen things up. If you need to verify put 15 rounds in the 30s and see if they still give you trouble, if yes I dont know what I'm talking about. I have had 3 mpx have still have 2 including the one your shooting, have half a dozen different mag configurations, they just dont love the super stiff mag springs. Also check for burs on those metal mag lips, touching them up with a stone cant hurt if too sharp.

Edited January 9, 2020 by inertia

[ck1]

I definitely agree with loading newer mags up and letting them sit for a few days, that’ll let them settle in and I bet they’ll run better. All of my mags have the +11 TTI base pad extensions with their included extra power springs and I’ve never had an issue (though I always run them at 40 instead of 41 unless I’m starting a run, because 40 always works on a closed bolt but 41 can be iffy... if it’s a bolt-closed start it’s 40, not 41)

 

Edited January 9, 2020 by ck1

[2011BLDR]

Are you  sure they are Gen 2 magazines (tan follewer ) ? Gen 1 mags can be iffy in some gen 2/pcc guns....

[smoker 01]

Yes they are with a tan follewer

I put 30 rounds in them and put them down for a day or two and try them on friday

I will let you know

Thanks

[smoker 01]

Ok

I did load my 30 rounds mags up and left these for 2 days

Also made the bolt as wet as it could be with good oil

And......

No more problems with the big 30 rounds mags

PF range from 128 to 148 no problems anymore and bolt locking back with all PF

PF 133-135 is by far the best to shoot and yes the 115  are better to shoot then the 124

I gonna try the 145 and let all know

Thanks for all the response !!!

[inertia]

Bingo MPX 30s are just a little over sprung when new, breakin usually resolves though most of us throw extensions on anyway.