Well "kick" could be more correctly referred to as "felt recoil" (which, of course is subjective, i.e. not all people perceive it the same way). As far as the size of the hole (permanent wound cavity) it puts in someone's body, bullet design (FMJ, JHP, etc.) is going to be a big factor. All things except caliber being equal, among the "service calibers" (9, .40, .45, .357 SIG, etc.) there really won't be a significant difference. Certainly not enough to definitively say that "caliber 'X' will consistently do a better job of dropping someone than caliber 'Y' would." AFAIC, "stopping power" and "knockdown power" are terms that need to disappear from the lexicon of the gun culture.
So...to put you on the spot for a sec Matt I'll play devil's advocate here...if you can't say "stopping power" or "knockdown power"...why is it that a .22 is insufficient for self-defense? What doesn't it have?
Kind of like how horse-power has no correlation with horses and aside from sounding very impressive in the early twentieth century when horses were still a more common mode of transport than automobiles, holds no informative value (the specification labeled horsepower describes how rapidly the engine produces torque at a specific RPM). Anyone who thinks that their 52 horsepower Geo Metro has the equivallent power of 52 actual draft horses will be sorely disappointed to find that one draft horse can out-pull their little car. Daniel
Few reasons... -.22 ammo can have reliability issues compared center-fire ammo (lots of "duds"). This is particularly true if you use the cheaper stuff. -the rimmed cartridge design can cause issues in auto-loader magazines (rims "locking" together) -insufficient penetration can be an issue, particularly when shooting short-barreled pistols and revolvers (i.e. snubbie revolvers, small autos like the beretta 21, etc.). Is a .22 better than a sharp stick? Yes Would I carry one if that was all that was available? Yes Would I carry one or recommend one if there was something better (i.e. a "service caliber") available? No
Sufficient mass and force at impact to cause significant trauma that's likely to effectively incapacitate an adversary. Sure, with the right shot placement, it'll do the job... but when I look at police shooting stats, I'm not too hopeful for people to effectively place their shots under pressure.
That says it all. Except maybe those who have physical problems where they cannot really use anything else as for firearms. Say those with severe arthritis or neurological disorders. Then maybe a tip up Berreta 21 in .22 might be a good bet. But for the rest of us, yes pick a more serious cartridge and platform. Deaf
For me: Glock 23 with SXT's, or Smith Mod. 36 with hydro-shocks (one reload each) when off Post. Spyderco Police with grip tape or something similar. Surefire 3P Hands and feet