I beg to differ, on two points---
I think one would be better off with whichever .22 LR SOLID would function best--Preferably a high velocity, such as CCI MiniMag or the Remington Thunderbolt.
Feeding is a bit more reliable with solids, and you want sure and certain penetration. There seems to be a consensus that the HPs do not penetrate very well into the skulls of steers in slaughterhouse and while finishing off wounded deer. I would figure that a steer's skull would be significantly thicker than a human's, but not a whitetail deer's skull.
I think he best training would be three or four into the chest first, and then instantly going for the eye sockets. The head and neck are very mobile and very quick to jerk aside and dodge. The justification for shooting a human in the first place is if he is already doing something agressive and violent, and is thus already into an action mode. The "Mozambique Drill" is two to the body and one to the head. Those chest hits might slow things down, even if they aren't instant stoppers.
A situation where the head is holding still with the owner pretty much unaware of a MK II (not a small, sneaky handgun) is more of an ambush than a defensive situation . When we tell one another about the mob and the Mossad using .22 LRs, we are really describing executions or assassinations, not defensive shootings.
A few good chest hits with good penetration, even if not immediately incapacitating, are far superior to clean misses or marginal, glancing hits to the head.
I realize this is a rather grisly conversation, but let's be realistic, especially if discussing saving the life of a loved one.
Best regards---
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---The Second Amendment ensures the rest of the Bill of Rights---