I belive that in PA it's 270 or bigger but I may be wrong. In Colorado a 243 is legal and in some states there are no caliber restrictions at all. You can hunt elk with a 25-20 or 22 Hornet. Just because it's legal doesn't make it a good idea.

The unarmed man is not only defenseless, he is also contemptible.
Niccolo Machiavelli