You're not getting it Ron. When you load a .454 ball you're shaving the excess off. I said swaging, I guess that wasn't exactly right. The point is if a .451 fits tight the .454 isn't going to be any tighter and as for extra mass it's negligible.
However if you have a .451 that only shaves a thin ring it may move under recoil and lock your cylinder up. Some guns can get by with a .451 but of my three only one can. The Pietta manual that came with my 60 Colt recommends a .454 ball.