After seeing a several dozen postmortem handgun wounds in two and four-legged critters and studying (and sometimes writing) the after-action reports, I have come to think of it all like this.
Your handgun is little more than a remotely-operated punch, the same diameter as your chosen handgun round. It pokes its hole and withdraws instantly. We can play with the tip a little bit; chalk it, change its diameter, make it round or flat, drill a hole in it or whatever. Generally speaking, think of the mouseguns as poking a hole like a small knitting needle; the 38/9's at a 3/8" dowel at best and the 40-45 class as half-inch dowels.
The worst thing you can do is limit the depth it penetrates into, or through, your adversary. The second worst thing you can do is place it poorly. The third worst thing you can do is make too small of a hole in him.
If you miss his/its CNS and/or support structures, you can't expect immediate incapacitation. Some people & critters just won't acknowledge having random holes poked in them. With bipeds, he closer you poke that hole to the centerline of the body, the quicker you get their attention.
At typical handgun velocities, the most advanced bullet technology cannot and will not compensate for three inches of lateral dispersion, from the centerline of the human torso.