I'm not so sure the barrel temp is a cause for copper fouling. IMO I think it is more of the roughness of the rifling which causes the copper to collect in the recesses much like wood dust collects in sandpaper. I have one Browning that is terrible for copper fouling. And this is even after going through a break in procedure. The best thing I've found that isn't harsh is Hoppe's Elite metal fouling remover.