For the folks that have unwanted visitors to their birdfeeder, but don’t want the expense of an air-rifle .22 CB caps are a great alternative. At about 2/3’s the velocity and 1/2 the energy of a .22 short they’re obviously intended for very small game up close, but they’re clearly not toys. They come in either long or short and when fired from a rifle make less noise than most air-rifles. You’ll want to shoot a few thru any rifle you intend to use to be sure that it will group with them. But, if you find a rifle that will group you can dispatch squirrel sized problems so quietly even your closest neighbors won’t have any hint.
I have an old Remington 550-1 autoloader that will normally cycle with short CB caps and if I do my part, it magically transforms bird food thieves into coyote treats with every pull of the trigger.
I have an old Remington autoloader which will cycle shorts, longs, and long rifles, interchangeably and with total reliability.
I never tried CB caps in it tho.
Getting one to do that seems pretty remarkable to me.