@Shadow Daedalus: Kiritsugu was effective because he was trained in eliminating magi, he had the Origin Bullets, he was unexpected, and he played
extremely dirty. He had a good understanding of magecraft on top of that.
Just using a gun is surprising since a mage isn't going to expect it, but just using a gun isn't good enough to give you an advantage. Volumen Hydragyrum would have blocked
any other bullets, and the same goes for your average defensive bounded fields. Reinforcing your body can let you dodge pretty effectively too.
Basically, if you want to make a Magus Hunter who uses guns, they
need to have understanding of Magecraft and training in how to kill magi
and also cheat all the time.