You need to do a couple of things...Find a gun smith that has a bore scope and have him look at the barrel to see if there is really a serious build up in it...
I had one look at my CZ .204 and he found about eight inches of powder residue that was cooked to the barrel (I bought it used)...Took quite a bit of scrubbing to get it 'clean'...
Secondly, make a practice of wiping down your cleaning rod between passes, and/or changes of tips...You can get a transfer from the previous application of solvent/debris on the rod and then deposit it back in the barrel from the rod..
Especially if you are using a brass brush and copper solvent..It will drive you nuts trying to get it all out..
