Toby,

I agree the legal minimum calibres aren't always needed, but sometimes they are.

Regarding a buffaloes skull being similar to a cow's, I suggest you check out Mark Sullivan's first video - "Africa's Black Death" - which started his video "success". He shoots a cape buffalo during a charge in the head, only just missing the brain, the bull hardly notices it, and the second barrel's bullet finally striking the brain, with MS having to jump out of the way to avoid the bull falling on him. Calibre was a .450/400 from memory.