I have an old crosman co2 8 shot pellet gun that I had to resurrect after having a squirrel problem a few weeks ago. It's only rated at 450 fps so its really just to scare them off. It's just as effective shooting blanks to scare off homeless cats, and the girls don't seem to mind the noise. Not the most accurate thing either, so Ive been considering the whisper or the big cat as an alternative. They are both single crank / co2 free so that's a plus too.