Reading all the "Gee my MPX runs dirty" comments/threads has me confused and concerned....

I thought the whole point of a short-stroke piston 9mm would be running *CLEAN* - like the AUG/FS2000/Adams AR/whatnot seem to.  Are you MPX owners really saying this thing is blowback-dirty (like a 9mm AR)?????????  If so is that just the folks running cans or everyone or well, really, just WTF? Or am I reading too much into this...

Thanks in advance!

It is interesting. Ron Williams made a 9mm upper that had to be handloaded for since factory 9mm was so dirty that it would impede function very quickly. Of course Ron's upper was straight direct impingement.  

 

If your referring to my posts over a few threads... I've been saying its running dirty when suppressed. I also shoot left handed so when block back is excessive in a gun I will know by the crap hitting my face. The gun while dirty still functions well past the 1k round mark suppressed so if it still runs who cares if its dirty.

Just means pushing off the caked on carbon buildup.

All guns run dirty suppressed anyways. If Sig managed to fix that they have pulled off a miracle. Dirty isn't a problem anyways, proper lubrication is.

Well, I ran a comparison today - put ~100rds each through an MPX and a CMMG 9mm blowback AR 7.5" pistol running a Spikes ST-9X buffer and a carbine spring (along with the CMMG 9mm bolt of course).  Same UMC Green Box in both, same boxes even - run 15 in the MPX then 15 in the AR, etc.  Afterwards, stripped them each down and cleaned them.  Neither suppressed, just an A2 style FH on the end.  Oh, and I cleaned them both beforehand, so they started "clean" by my standards.

There's no other way to say this .... the MPX is freaking FILTHY.  Took WAY more patches and they were COMPLETELY black  Now I'm "that guy" when it comes to cleaning it seems, so I removed the MPX barrel, cleaned the gas cylinder and piston, etc.  But there's no escaping the fact that the MPX got way, way, dirtier.  Some of that is the whole locking bolt thing - there's locking lugs which get dirty in the MPX, while in the AR there's just a chamber and a bolt face.  I'd say the two bolts were about even on filth, but the MPX upper receiver was just a mess.  I was about ready to dunk the whole damn thing in the ultrasonic cleaner and call it done!  As I mentioned, I run several other piston guns in .223 and .308 and *NONE* of them come anywhere near close to this level of dirty, so I don't know what SIG has done with the MPX, but they've done something .... interesting.

I didn't run the two guns to failure, so I can't say whether the MPX "cared" less about being dirty, but just from an owner/operator cleaning up after shooting perspective, the MPX is *NOT* an improvement  I'll try and post an overall comparison later, but there are definite advantages to the MPX - felt recoil is way different without the huge reciprocating mass of the blowback gun, modularity is impressive, etc.  So it's not like the MPX is worthless, just not cleaner.

Anyway, now you know

Thanks for your insight.

Could someone please post pics how to disassemble the MPX gas piston system ?

It's in TFM - I could probably snap pictures next time, but if you have the barrel in hand (remove from upper receiver), you'll see a tube with a hex(?) shaped end.  The end of the hex-shaped piece (I'll call it the plug) has a center hole and two smaller holes.  The "body" has a single hole at what we'll call 12 o'clock. This is the hole TFM is referring to, drop the end of a punch in there (I use brass ones 'cuz I'm anal) and rotate the hole to almost 9 o'clock or 3 o'clock (I don't recall if it moves both ways, sorry).  You should see now that there's a ridge or lip which holds the "plug" in place, you should be able to turn the plug by hand now to get the lip completely clear - at which point the plug can be wiggled free.  It's being held in by some gas rings, so the fit is TIGHT.  I seem to end up tapping on the protruding part of the piston (TFM calls it the "tappet") to push the thing out, but I think it could be wiggled free.  

Once the plug is out, you'll need to gently drive the piston/tappet out and then you'll have the 3 pieces shown in TFM in your hands.

Re-assembly is in the reverse order - you'll likely have to tap the piston/tappet in (gas rings there too) and align the plug/body so the lip is clear before tapping it to seat it.  Then rotate the plug body so the hole is at 12 o'clock again - it will click into place and you're done.

HTH

Thank you for the info.  

Could you please post a pic and point to the hole that is used for the punch?

Thank you