IMO, 243 is a little light to be dependable on the northend of a southbound 300lber. Yet if the buck is unalarmed and broadside, a 243 will drop them as good as anything. A 25-06 with a quality 115-120gr bullet is a big step up. Anything above that and you are golden. Like others have said, shot placement and a dependable bullet are key. Flat shooting calibers are nice in many areas.
