I used a bore mop and "FLITZ" metal polish (not very abrasive) to polish the chamber of my AR shorty AFTER the chamber brush and solvent cleaning.
WOW!!!
The mop came out completely black after only a few seconds in a slow rotation hand-drill.
I cleaned the mop and ran it in a few more seconds, black again.
Do these chambers get that filthy?
The chmaber brush doesn't seem to do too good a job other than "knocking off the big chunks".

I've used "FLITZ" for years to polish chambers and it has always worked well.
But using it in the AR shows me how the chamber walls can get clogged with garbage.

What do you think?

I do the same thing. It does a couple of things, cleans and polishes the chamber, increases reliability by reducing the chance of FTEs. I just try not to go too crazy in there. I only wish that I could find the special rod and mop I had made up JUST for doing ARs. Oh well.

How often do you do this, and have you noticed real results, ie, sticky chamber and this fixed it?

That black will appear even if the metal is perfectly clean.  You have removed a tiny amount of metal which appears as black on your mop.  Try it on a clean piece of steel, brass or aluminum.  It will come out black then too.

Quoted: That black will appear even if the metal is perfectly clean.  You have removed a tiny amount of metal which appears as black on your mop.  Try it on a clean piece of steel, brass or aluminum.  It will come out black then too.

i'll second that. it's just minute particles of metal being removed.  i notice this when i polish feed ramps.

be C A R E F U L when polishing, cuz if you polish so much that you are removing a LOT of metal, you can't put it back.  just make it shiny  and /or smooth, and let it be.

(brought to you by the Dremel corp, "at dremel, we, in the hands of the inexperienced have destroyed more firearms, than moisture, thieves and the brady bunch combined"
just a word of acution, sure you've heard it already, though.

I have used flitz in the past to polish up the feed ramps in my pistols, it works fine and because of its very minor abrasiveness it avoids the, oh shit! I screwed up my gun issue.