If it was walkin away i wouldn't shoot it. Simply grunt or bleat at it and it at least turn enough to give you a decetn qaurtering away shot. Just remember with a 30-30 you dont quite have the distance. It was designed to be more of a brush gun. I dont know what your max distance is but i wouldn't push much over 100-150 yards.
If he his standing broadside put it right begind his shoulder bladewhere it meets about 6 inches from the belly.