My approach to your question. . the goal of shooting someone in self defense is not to kill him, but to stop him from pressing his fight or invasion. A person shot with any caliber may stop his activities not wanting to be shot again. Good. A percentage won’t stop, and then you need something that is more likely to stop the aggressor than a .22,.25 or a .32 all of which will kill but might take several days. Many defenders have been killed by the person they shot who ultimately dies. There are lots of studies on line and reputable articles ( i was reading one a few hrs ago about using a .36 cal cap and ball for self defense) you can read and examine use for SD of various calibers , .380 and up, and experiences with them. And wouldn’t a 40 grain projectile with no cross sectional density to speak of at .22, traveling at 1200 fps, punch right through a wall? In lieu of that .22 revolver, i might suggest a .38 special revolver with a 4” barrel and low flash powder, or maybe even a pump shotgun with a barrel between 18-20”. But, everyone has an opinion. I am glad for you your are thinking about this. Happy thanksgiving.