RE: Best .22 LR groundhog ammo?
I've used quite a variety of .22 ammo for g-hogs. My favorite used to be Winchester 40 grain PowerPoints (hollow point). Lately I've been using CCI subsonic hollow-points - very accurate & quieter. If you're looking for ammo to go hunting, here's what I would look for:
1. Accurate in your gun - buy a couple different brands and find out what your gun likes
2. Hollow point - I'd for sure get a hollowpoint design instead of round nose.
Whatever you choose, I'd aim for the head whenever possible. The .22lr isn't always going to kill something as big as a groundhog instantly if you shoot it in the body. The stingers you have should do a number on them at the ranges you are talking about.