I agree with the IC being great for most shotgunning.. It or an mod. are about as tight as I want in a shotgun except for gobblers.. As for shooting squirrel, I had friends in W. Va. that used to do a lot of tree squirrel hunting before their country was developed for big city interests.. They felt squirrel shotguns should be full choke due to the small size of the animal and tough hide.. They felt a squirrel could soak up more shot for its size than a rabbit or grouse..
