Some guns you can switch between cast and copper and there's no real issue. Those usually aren't your best shooters to start with. Others want nothing but cast and then if you put copper down the tube it takes a while to get them to settle in. Most of my guns that I shoot cast in at all I shoot exclusively with cast. There are a few that swing either way and some that only get copper. The swingers tend to be the guns that only do 2 - 2 1/2" on a good day in the first place.