MPX Reliability @ 12k+ Rounds + Maintenance Schedule?

[SDchillin]

I figured this may be interesting to some: I have a MPX PCC Competition(?) model that recently has crossed the 12k round mark with zero piston maintenance. Reliability has been about 99%. As long as the bcg is cleaned/lubed and the firing pin channel is clean and dry, she's been running consistently.

 

The BCG assembly has been cleaned and lubed regularly and the upper receiver has had some of the more severe carbon buildup removed, including in the barrel extension area but truly minimal cleaning overall. No parts replacement yet. I'm really impressed with its reliability so far between 115/124gr factory ammo and some big brand 124gr reloads.

 

That being said, I understand that I'm potentially forcing a failure at this point. I have an In Lead We Trust maintenance kit here plus some extras and I'm ready to pull the barrel/piston and soak it in kroil or throw it in a sonic cleaner if I have to in order to get it disassembled.

 

Can you guys please give me some advice on what parts should be replaced at this point in light of the round count? I was going to at least order a trigger scale to stay on top of extractor tension.

 

And any ideas in case the piston assembly is bound up?

 

Thanks!

Edited June 18 by SDchillin

[Chillywig]

On 6/18/2024 at 6:08 AM, SDchillin said:

And any ideas in case the piston assembly is bound up?

 

Thanks!

Did you get it apart? How bad was it? 

[SDchillin]

On 7/5/2024 at 6:41 AM, Chillywig said:

Did you get it apart? How bad was it? 

 

I got it apart. Really didn't take much, surprisingly. Had to twist the tappet with a wrench a bit, it wouldn't go by hand, and the piston tapped right out with a gunsmithing hammer and punch.

 

I replaced the firing pin, fp spring, extractor (and all related components), replaced piston + tappet (out of convenience and will clean the dirty ones for next swap) and the recoil springs. She's running like a top now.

 

Called Robert at ILWT, explained to him what I put the gun through and he said I could drill out the gas port with a 3/32" drill bit to remove carbon if needed but I haven't done that yet as it's running fine still. He also said to check the back of the bolt lugs for burrs and knock them down with a file if they were present but I didn't see any. 

 

Let me see if I can resize and attach these pictures I took of the piston & tappet during disassembly.

Edited July 27 by SDchillin