[Mello2u]

This "one-shot stopping power" holy grail thing might be just a mirage. It is one of those things that would be nice to know, if it existed.

How many here have had professional training in defensive handguns?

Of those, how many have been taught to shoot once and only once?

In the two places where I have been trained the training is/was (assuming a single threat): Shoot twice to center of mass, assess, and proceed as necessary.

A handgun is a compromise, that is hopefully "good enough" to get the job done. That job is to incapacitate an imminent threat of great bodily harm or death as quickly as possible.

It is not about lethality.
It is about stopping the threat.

It is irrelevant whether the threat dies sometime in the distant future. Merely firing a handgun is legally using deadly force in most jurisdictions. It is relevant whether the threat is able to bring its attack to you and do you great harm.