You ask what is a good gun for American animals. Well we dont have many monsters here, Moose and Bear is about as big as they come. the 300s are good all around, yet sometime a little big for whitetail.
30-06, 270, 308 are good for most anything you will see here. I tend to use my 30-06 most of the time. I recently got a 300win for elk and bear.