To Remove Copper Fouling, Try this:
1/3 ea. White Vinegar, Hydrogen Peroxide & 10% Ammonia.
You can get it All at WalMart.
Way Cheaper than "Bore Cleaners" & it Works Great.
Do Not Use w/ a Bronze Brush, Use a Nylon Brush.
It Will Eat Up your Bronze Bore Brush.
Usually 4-5 Passes w/ a Wet Brush, Let it Set for 5 min & Run 2-3 Dry Patches.
No More Copper! Then Run a Tight Patch Soaked in Ed's Red thru the Bore.
Follow w/ a Dry Patch & your Done.
UncleSarge58