I know most will have a heart attack about this but... try a stainless steel bore brush if its bothering you that bad. Get some Boretech Eliminator, its a surfectant and will lift carbon, copper....
Stainless brushes are softer then barrel steel and won't hurt them, let the barrel soak for about 15 mins, scrub and then patch it out.
I see the world thru bloodshot eyes
Streets filled with blood from distant lies
The dogs of war never compromise,
No time for rearranging.