the #9 up to even the #12 are very small
Don't the shot sizes get smaller as the number goes up? Typical bird/small game shot is #6-8 & is much larger than the #12 used in .22 shells
#12 shot in a .22 is usable for starlings, etc. at 10-15 feet. Granddad used it all the time to keep them out of the cherry tree.
Yes. #12 shot is very small. It almost looks like sand to me. in a .410 even, I wouldn't use it beyond the same range. In a .22, you have a long bbl that will help control the shot pattern. With a 4" rifled bbl, the shot pattern opens up FAST. It'd hard to get more that 10 or 15 pellets on a pop can at 15 feet with that short of bbl.
The small shot is most often chosen for the .410 pistols because, like I mentioned above, for snake shootin'. But, you have to be close. Too close for me. I stand off a bit further and use something heavier, like the #6 or #8. Better yet, use a .45 Colt.