We are talking "ground Squirrels" right? (wood chucks, tiny little things that have spots/stripes on their backs, something the size of a rat)
I can't believe some of the responses if they are serious. Really hard to kill little buggers
, killed them all the time with my Daisy BB gun. Bout 7 pumps did just fine. A .22 round has the greatest projectile vs animal ratio that I can think of and we are worrying about things like penetration? A .22 short is more than "enough gun" for a ground squirrel.
As far as the origional post, It doesn't matter!! Hit him with whatever you have and it will be fine. But that is the key isn't it? You have to hit him. It doesn't matter what you shoot at him with if you don't hit him.
Might want to break out the ole thirty'n-ought-six just in case...if you're worried about a one shot kill.
