Cast performance bullets are good quality for a cast bullet, but don't expect good results on heavy bone such as skulls, shoulders, leg bones and spines. We are talking about 150 year old technology that was long ago replaced by FMJ steel-lined solids at 2150 fps to achieve adequate penetration on the tough stuff.

That being said, I am sure you can kill a buffalo with a .222 if you are determined to do it.