For working up a hunting load, if you want to be meticulous, you want to replicate the condition your bore will be in on your first shot at game. I hunt with a clean dry bore. My gun is not fussy about the first shot on a clean bore or the 5th shot on a "dirty bore though, so I don't worry about it.

You have to figure out if you will hunt with a clean bore or a fouled (once-shot, or maybe just powder fouled) bore. Then, replicate that condition at the range. You may find you don't get differing point of impact with clean vs. fouled. You may be able to shoot 2, 3, 4, or more times without affecting point of impact. Just have to try it and see.