Oh do I have what you need.
It's a German made RS in 9mm rimfire. Single shot, smooth bore and factory ammo is available. They were/are popular in Europe for pests and scaled down indoor skeet shooting. Used to be popular here for clearing the garden of snakes, birds and such. Guess cities got uptight about folks blasting our feathery friends in their neighborhood backyards, and they lost popularity. Lot more and bigger pellets than from a .22, but not the range or noise issues of a .410. Nice little pop and the 6 or 9 shot sized loads should handle most small nuisances.
Here is how the shell compares to a regular 9mm and a .22LR
That is super sweet!
ooo wee! i love it!
though at a glance not exactly cheap to feed.