I have seen buff in the bush and they are very, very, very large. A 30-06, even with 220 gr is not enough gun. 375 H and H would be my choice. I appreciate that you do not feel recoil in the hunting moment, but you are much more likely to be zeroed accurately and fire without flinching than if you use a monster caliber. Open sights would help if the animal was right on top of you, but less accurate than a scope. You very often see poor first shots on U-tube with un-scoped monster doubles.