... .22's are already so quiet, why would you want to add the weight of a can? ...
(1) - Because I'm lazy. I like shooting all of the squirrels I want to shoot (generally 2 or 3) all from one sit... Eley Subsonic HP's or GemTech Subsonics... Not Hollywood "mouse fart" quiet. But quiet enough that they don't generally scare the other squirrels out of a tree.
(2) - Shooting a suppressed .22 rifle is an excellent way to start new shooters.
(3) - It's fun...
