Here is the way I see it copper is not the problem most of the time.
In a clean barrel your first bullet will leave some copper fowling but what follows the bullet?
Yes all the dirty hot burnt powder coating the barrel over the copper so your second
shot is riding on top of the carbon in your barrel and adding more each shot. Copper will not coat the carbon. There fore you will have less copper than you will have carbon to clean out. the copper cleaners do a pretty good job getting the copper out but you have to get the carbon out first and there is nothing that will cut out the carbon better than wire brushs kroil mixed with Buctches boreshine and patches.