There is big ranch not too far from here called Thunder Hills. They have trophy buffalo hunts, and some folks do it with blackpowder as well as archery. I have heard that arrows and big conicals are very effective on this big beasts, and high velocity CF rifles like the 7 Rem Mag are not. You might do a search on Thunder Hills Buffalo Ranch, or something similar - don't remember for sure - but they have a website with a lot of info.