I shot squirrels all the time with subsonice .22 ammo. I think I might be using paper boxed CCI or maybe Aguila rounds. If the first shot doesn’t kill them I give a second shot to the head - which is usually necessary.
I do, too. They’re not native here and a very invasive and destructive species.
Some idiot apparently thought they were cute and released them.
Fair number of houses burn down from these rodents chewing electric lines.