Buffs are odd critters , they tend to absorb copiuos amounts of lead with no ill effects at times , and other times one shot will take 'em down ..
I have seen both extremes , one shot with a 375 , and six with a 600NE ..
I had a 470 NE dubble that accounted for one , a 500 NE double that accounted for one , and my Lott's have taken four ..
Regardless of choice , brings lots of ammo , you'll probably need it ..
If a bolt gun , a big magazine helps , my Lott is a six shooter ..
I would not go smaller than a 416 .. otherwise as much as you can handle bore wise ..