Camofish-
a .243 will be fine - i bagged my 1st mulie 2pt. @ 15 years old with a bolt action Remington .243 winchester and the buck went down fast w/ one shot. She'll be fine on mulies.. My father also bagged a cow elk with the same gun w/ no problems. He did have a hotter round for that elk though. We use a 85 grain round for the mulies. It is the most accurate round we've found for that particular gun. I think accuracy is most important if you want to take down a animal quickly.