When we were raising and killing Hampshire hogs on my parents farm, a single 22lr from a single shot rifle would do the trick. But ONLY if you can be directly in front of the hog and aim for a sunken spot directly between his eyes or slightly above. I have been told that an ear shot directed straight through would do the same thing. My 44 mag Winchester '94 has been on many wild hog hunts with me. I have never had one I shot get away. The straight on head shot has never failed me. Most don't even squeal more than once. The smaller the hog the easier the shot and the more tender the meat.
Edited to add:
If you use the straight on head shot. After the hog goes down, if he / she is laying on his side still kicking like he's trying to run away leave him alone. That's a natural nervous reaction.
Good luck.