I had a .410 - worse bloody excuse for a shotgun there is.
I would put a limit on 28 bore as being the smallest effective gun for hunting anything but small birds.
I sold it after 3 years of poor results on grouse using 7 1/2's and 6's, 2 1/2" and 3".
I didn't try #4 shot, which I am told makes the .410 usable.
Lining that single shot in .22 LR would make it at least usable.