When I was a little guy they would shoot the hogs in the eye or ear with a 22 to butcher them. We always used a small sledge hammer with a spike welded on the face. I remeber going to other farms to help butcher hogs where they used the 22. Sometimes they would go right down, sometimes they had to shoot them many times in the head to put them down. I wouldn't do it just because the animal could suffer a good deal of pain if it didn't put him down.
One thing you may want to considder is the little guys can still rip your calf muscle to the bone. I would personally be kind of soar with a fellar that knocked a plug out of my head. Bear in mind a wild animal has a flight or fight instinct. I would much rather face a very tough man than a little pig with 2" teeth that are designed to rip flesh. Just a thought.
Blessings