Let's differentiate between a hog killed in a pen (as at a slaughter house), a hog killed hunting, and a hog that is trying to gore you.
Hogs killed at slaughter houses are penned in and thus a .22 will do fine in the noggen.
Hogs killed hunting are a bit harder but usually you are shooting them at a distance and they are unaware of you.
But hogs that are trying to defend their babies are a whole different kettle of fish (as is any animal, including humans.)
Now the original poster was worried about being charged by a enraged hog and not some penned in critter waiting to be slaughtered.
I suggest going to the board:
and reading all about hog hunting and what happens out there.