In order to increase capacity the fix for the rimmed head of .22 LR was to make a huge banana curve. It worked for rifle but pistol it was obtrusive.
Several pistol makers made slots in the upper 1/3 of the magazine body to allow the rimmed case to drop parallel to the rest of the rounds, which allows more, it sort of staggers the rounds.
Well we all want more....
Advantage arms makes 15 round mags for the drop in kits or you can make them yourself.
i'll check them out.... sounds like if someone were to create a high cap 22lr semi auto pistol, the market is wide open.