Look up KG-12, works good to remove copper fouling

KG-1 for removal of powder and lead fouling.
KG-2 for removal of copper and lead fouling, also works well for polishing bore (1200-1400 grit).
KG-12 for aggressive removal of copper fouling.
KG-3 solvent and degreaser for removing fouling loosened by KG-1, KG-2 and KG-12.
KG-4 gun oil for protecting metal that has been cleaned and degreased with KG-3. Meets military specification Mil-L-63460 D.

Check out this link, very good info
KG-12 Copper Remover - KG12 Removes heavy copper fouling quickly from rifles without ammonia, restores accuracy to 204 Ruger, 223 Remington, 22-250, 220 Swift, and all other high velocity rifles

There are other products out there that work, but this is what I use.