I've seen a 9mm shot barrel made for the Savage 220 shotgun; there were a few sold by Numrich Arms Co. when they sold off all the remaining odd lots of 219/220 barrels from the Savage plant in Utica. Probably made for potential export, I would guess, possibly even actually exported. Saw some other rimfires then, too (.310 Rem, 5mm Rem, .22 WRM--pretty clearly experimentals). Before then, Savage and other US mfrs. seemed to prefer the .32RF shot and .44XL shot for their versions of the "garden gun"--lots of mfrs. made small single shots for those, even a very few Win 1885s, I think.
I have a Peiper hammer "Cape gun" with a 2" .410 barrel and a rifled .44WCF barrel that you could shoot .44XL in if you wanted a wide pattern (and patchy).
Italian makers used to make special little shotguns for lark hunting! (What a lark!).
