I woud use slugs if possible, if not, #1 buck. I killed a deer in my younger days w/#4 buck out of a .12ga. Dropped it on the spot at about 40 yards. I still can't figure out how that deer died, not one pellet penetrated more than about 1-2.5 inches. a few hit lung but after seeing deer hit better with rifles and not going down, I can't for the life of me see how this one didn't high tail it never to be found. my tests with ballistic gel show that i wouldn't get much better results w/larger buck, until you get to OO, OOO, then your patterns are crap. I'm sure this will start a flame war and there are many dead deer to prove my opinions wrong but I don't like buckshot.