GRF,
The pass-through point is a major one when hunting buffalo in herds. A good friend, another gun writer who really likes lever-actions, chose a .45-70 with high-quality "solid" bullets for his first buffalo hunt in Zimbabwe. It was in thick cover, and he killed a good bull--and also an unseen cow behind the bull. Luckily the bullet landed in the right place on the cow too.
The first bullet I put into a Cape buffalo was a 300-grain Fail Safe from a .375 H&H--which in my experience worked a LOT like Barnes Xs. Luckily it was in pretty open country in Botswana, and there were two big bulls at the end of a walking herd of 250 or so. Russ whispered for me to make sure the bulls weren't in line with each other before I shot.
I aimed at the shoulder when the bull paused, but he started walking again just as I pulled the trigger. The bullet landed just behind the shoulders but went through both lungs--leaving an exit hole the size of my fist. Have hunted buffalo more than once since, and my experience (both my buffalo and those my companions have taken) is that an expanding bullet that DOESN'T exit is preferable, as most PHs have suggested.
They also might kill quicker, because in general a wider "mushroom" makes a bigger hole.
