A good deer bullet is a good wolf bullet. That simple. Everything else comes down to who's finger is on the trigger and where they put the bullet. A 223 is more than enough, but your shots will be limited and there's a good chance of a long track. A 7mm rem mag(my personal choice, and the choice of all 3 wolf guides that I know), 25-06, 30-06, 308 etc just opens up more shot possibilities with less tracking. Ultimately, it's whatever gun is the closest when you see one.