I di recall seeing an ad for 32 or 36 cal 'squirrel gun' in Fur-Fish-Game.
The co (I dont recall who) only made a few each year and the recommendation was to order early.
There was also an article about 'barking' your squirrel, that is to hit close to it and shock it to death.
Bob, just above mentions barking. I didnt see his article before I posted mine.