22 Magnum
I hadn’t originally planned to carry a mousegun for self defense (one with a considerably smaller caliber than a 9mm Luger), but there was a reason for it. Whether or not that is a good enough reason is yet to be seen.
North American Arms (NAA) .22 Magnum mini-revolver
My original mousegun was a North American Arms (NAA) .22 Magnum mini-revolver with the 1-5/8” barrel. I got it many years ago, before I had a reason to carry it.