22lr HPs were intended for small game hunting. Upon impact, increasing the diameter of the projectile. and turning a pin-punch into a ball peen hammer and more force per square inch. In the personal defensive scenario, the 22lr could be effective, but more effective in the hollow points than lead round nose, or even plated bullets. Less chance for skipping around skull bone and such. 22lr for SD? In a rather small percentage of situations I would imagine. Some will say it's better than nothing, but sometimes it may be like poking a grizzly bear with a stick. I like better odds, and if all I had between me and a grizzly bear was a stick, then I would run. Not that the 22lr wouldn't be effective, it just depends on what your thoughts are as to the definition of 'effective'. It should make most turn and run to stop being stung. The human head is a very small target, and mostly bone. I once made the mistake of shooting at a feral cat with my pellet rifle (spring action cocking..1000fps) and using pointed pellets. A direct head shot was effective enough to make it run very far away. Away from my property and my animals. Two weeks or so went by and I saw it again one day in the nearest town checking out a local car wash dumpster when I realized I should have used a flat point pellet instead. I'm just sayin'.