DO NOT TRY A HEAD ON HEAD SHOT! Their skull is much heavier than a Domestic cows. Go for the behind the ear shot ONLY if you are real close, and you are deffinately sure of the shot. Other wise go with a 500 grain bullet in the heart lung area with the 45-70. I have talked to, and went with several people that have shot Buffalo up here. We have a big herd at Delta, 80 miles south of here. That is one of the biggest hunts in the state. Having accompanied several poeple that got drawn and have killed them, I do know a little bit about the subject. It is hard to get close without being detected. Their skull is much heavier than a reguler domestic steer, or cow will have. Shots to the head will not work like it does with a domestic steer. Since you said it chases the owner if he tries driving it, the animal will probably come after you if you try to get close. I think the safest thing would be a heart lung shot, since the target is much bigger. You don't have to get as close, meaning you have a chance to remain undetected. At least you have a better chance to get away if you are seen. Up here the state requires that you use a gun that will retain over 2000lbs of energy at 100 yards to hunt Bison. That knocks out anything smaller than a 30-06. A 45-70 with a 400gr bullet gives 2372 ft lbs of energy at 100 yards. The neck is even a worse place to try a shot because you have a very small area to hit inside a massive neck. This animal is not like a deer, with a scrawney little neck, that you can hardly miss the spine in. There is a lot of heavy muscle around the spine, and a lot of hair, giving the false impression of where the neck really is. Good luck and go with the .300 or the 45-70. Both are good choices.