gunnut308 nailed it - .308 Win, 165 grain - boattails for the long shots if your rifle likes them.
I moved up to 165 gr after having some 150 gr fail to exit on large whitetails - the 165s go right on through: two holes = better blood trail.
I'm using a Kimber 84M Montana, .308, Leupold 2x7, Kimber bases - very light, accurate, versatile - but have been hunting in Adirondacks so no 400 yd shots! you might want something with a little heavier barrel if you want to go out that far.
