I certainly wouldn't use sandpaper to polish a chamber but I have polished the chambers on all my guns, using polishing compound and a bore mop. No idea if it helps anything but I see no evidence that it's hurt.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.