JCN’s reliable MPX PCC thread.

[JCN]

Primary data is here in this thread:

https://pistol-forum.com/showthread....=1#post1321249

I thought I would post a summary from 10k rounds on my MPX PCC:

Setup:
8” SBR Gen 2 MPX
150gr Syntech which chronos at ~1000 fps.
Stock gas system.
-25% recoil springs from In Lead We Trust.
30 round magazines with TTI basepads, stock springs.

General philosophy:
When shooting weaker than designed ammo, need softer springs in the system.
-25% recoil springs add back margin and reliability.
You could also get that with a larger gas port, but I’m going for gaming softness.

With a weaker spring, the gas system does have to be clean and the bolt clean and lubed to prevent malfunctions.
Weaker magazine spring tension helps too (stock springs with the extra length of the basepad) as the bolt system doesn’t have / store the energy to strip the next round efficiently with the weaker springs, so vet your mags and break them in as well.

This combination works with ridiculously weak mag springs as well. If the magazine is going to induce a FTL, it’ll be with a full or nearly full magazine most of the time. The flat nose 150 Syntech is probably the most vulnerable to that kind of malfunction in a way that round nose or copper plates is not. There’s a reason why Syntech PCC was made with a round nose. That being said, that’s the ammo I had sitting around so that’s what I tuned for.

[JCN]

@S Jenks was kind enough to share the MPX armorer’s manual recommended replacement intervals:

https://pistol-forum.com/showthread....=1#post1335312

The summary of that is:
5K extractor spring, firing pin spring
10k firing pin, bolt carrier group, gas piston and rings, recoil springs, hammer and trigger pins and springs
20k gas plug and it says barrel, haha.

For my practice upper, I’ve settled on the following:
Clean gas system with barrel in place: 2500 rounds.
Clean upper and bolt: 2500 rounds.

Replace extractor spring and donut: 5000 rounds.
Clean gas system with barrel removed: 5000 rounds.
Replace gas rings as needed: 5000 rounds.
Clean upper and bolt: 5000 rounds.

Clean gas system with barrel in place: 7500 rounds.
Clean upper and bolt: 7500 rounds.

Clean gas system with barrel removed: 10000 rounds.
Replace gas rings as needed: 10000 rounds.
Clean upper and bolt: 10000 rounds.

When I say “clean” it means that you actually confirm clean and not just go through motions. Whether it’s solvent or carbon picks, doesn’t matter. But make sure clean means clean.

That’s where I’m at.

For my match upper, instead of 2500 round increments, I’ll probably clean at 2000 round intervals to increase reliability. Also since it’s only <$5 of parts, I’ll probably replace the extractor spring and donut every 2000 rounds on my match upper.

Going forward, my replacement strategy might diverge a little from the factory manual. For the more expensive parts I might run until they break on the practice upper.

[JCN]

Factory recommendation:
5K extractor spring, firing pin spring
10k firing pin, bolt carrier group, gas piston and rings, recoil springs, hammer and trigger pins and springs
20k gas plug and it says barrel

I’m at 10k on my practice upper. I use the same lower for matches and practice.

I am going to replace cheap parts as insurance.

10000 rounds
1. Firing pin and spring.
2. Rings on piston and plug.
3. Hammer and trigger pins and springs.

[JCN]

A Dremel bullet shaped felt wheel to the feed ramps might be the ticket to give back some margin with flat nose bullets and high friction full mags with weaker recoil springs.

[JCN]

1. Bore snake the barrel.
2. Remove and wipe down the BCG
3. Oil the BCG.

[JCN]

Per others’ recommendation, having good luck with CLR cleaning of gas parts and following up with high temp anti-seize for the piston.

[JCN]

I would probably replace the extractor every 10k rounds or so as per the factory manual because this gun is sensitive to FTE.





New on left, worn 12k rounds on right.

[JCN]

I ran 11k rounds of Syntech with the -25% recoil springs.

It’s broken in nicely and now runs well with a fresh -13% spring with 130 power factor Eley PCC.

The -13% spring feels less optic dot bouncy than the -25% at this point.

[JCN]

One thing that may be lost on users of the MPX is that the gas system gets fouled pretty quickly.

REALLY quickly when using coated bullets like Syntech.

Like within 300 rounds there a noticeable increase in recoil impulse as the gas expansion chamber loses bolume as it gets coked up.

It’ll run fine… except that it starts blowing the cases off the extractor which makes ejection erratic.

For the first few hundred it’s super soft until that happens.

Using slower powders and total jackets, I could extend the cleaning period but I don’t reload.

Current setup is a restricted gas plug (0.469) and the -25% springs.

It’s not a problem of too little gas, it’s too much gas when the expansion chamber is plugged.

Using CLR and a mild steel 4.5mm drill bit to clean.

[JCN]

Some whiners whine like entitled spoiled brats.

Resourceful people create solutions…

If my reality is that I have to have fresh gas chambers often then I want the ability to change plugs easily.

Torch, vise, hammer and Allen key…



Voila





I can get the plug out from the front with just removing the front pin and handguard.

Theoretically less time than loading a mag….

Or a Limited shooter taking their mag apart and brushing it….