There are several power/velocity options between the CCI and Aguila quiet .22LR ammo.

My preference is for Aguila Super-Colibri out of a 16" bbl small rifle/carbine. Head shots _and_ thoracic cavity shots are deadly on squirrels out to 25 yards. I would limit to head shots on any bigger varmints.

Out of a 16" bbl, they are quieter than any air gun I have used that might have hte beef to kill a squirrel.