Depends on what "power" you feel comfortable using at the distance you find the squirrels. Some folks use pistols that have at least 500 fps (hopefully more) in .177 cal. (at least 7.9 gr. pellet) at very close range. Some folks use say 400 fps or more with .20 or .22 cal with at least 13-14.3 gr. pellet. Look at Crosman or AirArms, Falcon, but there are other makes as well. Go to https://www.crosman.com/get-hunting/hunting-with-airguns , this should get you on your way!...Good luck, it is fun!