Wiltshire is cleared for using .17HMR for fox, and to be honest on most outings its all I use. I find its a in between round i can shoot rabbits and then turn to foxes.
That said I don't use ballistic tip, I use CCI Gamepoint which is a 20gr round. And I ONLY head shots in or under 100 yards. That said i always have a mag of V-max just in case.