You shoot a buff the same as you do a deer, an antelope, etc. No difference.

If you screw up the first shot and have to face a charge, then you should know where the brain is and how to hit it, and books are good for that. The brain is just above and behind the eyes. When the buff has his head up, you can brain him by shooting up his nose. Or you can wait a bit and spine him as he lowers his head to hook you when he comes in close.

But if you put the first bullet one third up his body and into the crease at the back of his shoulder, just as you'd do with any other ungulate, you'll wreck his heart and aorta and never have to take another shot, except for insurance.