12/17 - UPDATE:    SOLVED...see my final post.

Thanks to all who replied.








Just purchased my first SBR in 300 AAC, and it happens to be a piston system from PWS.  I shot two boxes of ammo through it, and upon cleaning I noticed all this copper-colored shit all over the place inside the weapon.  It seemed to collect heavily on the very end of this piece (piston?)...




photo was taken AFTER cleaning it...it was worse than this.







In case you cant tell what that is from the photo above, its THIS thing...




I've never owned a piston-driven AR before, but I've never seen any of my other weapons do this,,so I'm wondering...IS THIS NORMAL??  
If not, is this cause for concern?

Any input is greatly appreciated.



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Not normal.  Looks like the piston is rubbing against the bore in the gas block.  Look there to see if you have any excessive wear marks.  If so contact the manufacturer for a fix/replacement.

Look WHERE??  I dont know what that is!!

New barrels do that for a few hundred rounds.

My wasr3 and FAL with new barrels shed copper for a few mags.

Inside of the gas block where the piston resides and the regulator.  See if there is excessive wear.  If not its must be the normal break in wear and should stop after a couple cleanings.

Will I have to remove the handguard to visualize what youre talking about?  Also, how does one recognize "excessive wear"?

I know just enough about gunsmithing to fuck something up!! These new-fangled handguards are a far cry from the plastic ones on my M16-A1 (issued by the USMC)!!

If you see a grove or the wear in only one area you have something out of alignment and its causing excessive wear where its contacting the other part.  If you have even wear through out the piston chamber and/or piston then your have a normal break in wear.   From you photo is seems as though you have a lot more wear than expected.

You should send your photo to the manufacturer since the have the expertise to diagnose the cause and solution.

Well I dont see "wear" on the piston...just a bunch of copper crap all over the end of it.  The metal underneath looks fine to me, but I'm no expert.  However, I forwarded a copy of the photo to PWS Customer Support.  Hopefully they'll get back to me soon.

I don't see any wear on your piston, just copper buildup.

ETA:  Just found this.  Looks to be normal for a PWS 300 BLK SBR:

http://www.thetruthaboutguns.com/2014/11/tyler-kee/gun-review-pws-mk-109/
"However, when I it came to the business end of the piston system, I was shocked at all the crud I found.

I assumed that I was dealing with some baked-on carbon, not unexpected given the operating conditions. But after much soaking and scrubbing with KG1, I found a much more insidious buildup of copper. Lots of it.

I’ll leave it up to our gunsmiths and technical wizards to tell me how that much copper accumulated on the end of the piston, but what I can tell you is that 20 minutes later, panting from exertion (mostly joking), I had finally managed to scrape away the copper leaving a clean piston. If you buy a MK109, I’d suggest you keep tabs on the end of the piston to see what your buildup looks like. It never seemed to affect the function of the gun, but it was certainly an oddity of sorts."

First off the piston and the gas block has nothing to do with this. How does the piston and gas block which has a nitride finish cause copper fouling (lol) .   The gas port that is drilled in the barrel has extra material on the backside hole . The bullet is scraping against the port  that cause the material to get pushed up into the gas block which is ending up on your piston .  (I have has this before on PWS and POF rifles).

This will go away after a few hundred rounds of shooting . If it doesn't it means the port has a really big burr and it needs to fixed or replaced.

THANK YOU, GENTLEMEN...GOOD TO KNOW!! (sort of...breaking out the KG 12)


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Received THIS...






Sure enough, after a soak overnight in KG 12, and a light buffing...

Good to see.  Considering that it's melonite (Isonite QPQ, etc), wonder if it'll probably take more than a few hundred rounds to break in the rough spots.

Either way, at least it's normal.