I forgot to mention that when using really effective ( Strong) copper solvents, don't use a brass brush. All that does is let you know the solvent works as it eats up your brush. I don't let a brush made of brass or stainless get into the bores of my rifles. Use the nylon brushes with a patch wrapped wround them and put some pressure on the bore. Clean the powder fouling from the bore and remove the traces of whatever solvent you use for that with acetone on a patch. Then clean the copper from the bore usng your special copper solvent, whatever it is.
When you are paid to clean the barrels of other folks rifles, as a gunsmith, you learn not to waste time on things that don't work.