Remember that the goal is to quickly stop an assailant before he can hurt you (or someone else). So the real question is how quickly and reliably being shot with a particular cartridge will force an attacker to stop whatever he is doing to try to hurt you (or someone else).
So while a .22 can certainly kill someone; but whether, if he's attacking you, a .22 will stop him quickly enough to keep him from hurting you badly is another question entirely.
There are four ways in which shooting someone stops him:
- psychological -- "I'm shot, it hurts, I don't want to get shot any more."
- massive blood loss depriving the muscles and brain of oxygen and thus significantly impairing their ability to function
- breaking major skeletal support structures
- damaging the central nervous system.
Depending on someone just giving up because he's been shot is iffy. Probably most fights are stopped that way, but some aren't; and there are no guarantees.
Breaking major skeletal structures can quickly impair mobility. But if the assailant has a gun, he can still shoot. And it will take a reasonably powerful round to reliably penetrate and break a large bone, like the pelvis.
Hits to the central nervous system are sure and quick, but the CNS presents a small and uncertain target. And sometimes significant penetration will be needed to reach it.
The most common and sure physiological way in which shooting someone stops him is blood loss -- depriving the brain and muscles of oxygen and nutrients, thus impairing the ability of the brain and muscles to function. Blood loss is facilitated by (1) large holes causing tissue damage; (2) getting the holes in the right places to damage major blood vessels or blood bearing organs; and (3) adequate penetration to get those holes into the blood vessels and organs which are fairly deep in the body. The problem is that blood loss takes time. People have continued to fight effectively when gravely, even mortally, wounded. So things that can speed up blood loss, more holes, bigger holes, better placed holes, etc., help.
So as a rule of thumb --
- More holes are better than fewer holes.
- Larger holes are better than smaller holes.
- Holes in the right places are better than holes in the wrong places.
- Holes that are deep enough are better than holes that aren't.
- There are no magic bullets.
The bottom line is that a lower power cartridge with a smaller caliber bullet will make smaller holes and may not be able to as reliably penetrate to where those holes need to be to be most effective.
Or to put it another way, why would anyone think that a .22 will be enough when sometimes a .357 Magnum isn't necessarily enough. LAPD Officer Stacy Lim
was shot in the chest with a .357 Magnum and still ran down her attacker, returned fire, killed him, survived, and ultimately was able to return to duty.