Get a brass rod before you ruin that barrel.
Good idea, but expensive. Since I have rifles of the same caliber, all we really need to do is bonk a lead ball a little into the muzzle of each then compare the rifling marks. If his are the same size as mine, it’s a .457-.460 barrel and we’re done.
I’ve got some hardwood dowels, but they really work best in much shorter barrels. If I have to use the metal rod I give it wrap in high strength packing tape first. That helps keep it centered better and keeps and steel from contacting steel. It’s still scary though, even with brass.