I use a remington 550-1 semiauto .22 with some ole crappy scope that I plan to replace some time in the near future. I've tried a 880 powerline daisy pellet gun rated at 670 fps...and while it took the squirrel down, he flopped around quite a bit...even after a few more close shots....some on here have used .177 caliber pellet guns without any problem, but I'll stick with my .22....clean...and over quick!! I have more range too..