Choosing a proper caliber

I was talking to a friend the other day and he asked me some ideas on what he should get for a rifle. He wanted a rifle that would be adequate for all game. Even though you could use some calibers for most game in North America such as; the .300 wm, .30/06, and varius other .30 caliber cartridges, it would be best to find the optimal caliber for hunting different types of game. For instance; you could use a .243 win for pronghorn, deer, sheep, goats, a .270 win for elk and black bear, and a .338wm for moose, brown bear, and bison. There are many cartridges that could be used to overlap different types of game animals, for example; a .270 wsm would be suitable with the right bullet for deer all the way up to moose. Although it would not be the first choice for moose hunting, it could do the job. A .300wm could be considered a little overkill for deer hunting, but with a 165 grain barnes bullet you could take anything from a deer to a moose. There are a multitude of calibers and bullets to fiddle with to find what you like and using the Federal ballistic software from their site is a great tool: