There are several factors in evaluating wounds and trauma caused by bullets.
First, there is a GIANT difference between administering a fatal wound and stopping someone from doing something instantly.
If someone is doing something so bad that I am moved to shoot them, I want them to stop doing it instantly.
Therefore, I want to transmit as much energy to their central nervous system and/or circulatory system as possible.
The mechanism which produces death from gunshot is mainly blood loss. As a secondary possibility, massive disruption of body systems can incapacitate before blood loss is a factor. “Shocking power” or hydrostatic shock is highly debatable.
If blood loss is stopped in time by medical treatment, even a “fatal” gunshot wound (or several) need not kill. However, infection from a non-sterile object pushing clothing, skin and whatever deep into the body is a very serious danger. Likewise, disruption or destruction of internal organs (the so-called “hamburger effect”) can cause the equivalent of a deady or fatal disease.
These are the rules for gunfighting:
1: have a gun.
2: a hole is better than no hole
3: more holes are better than one hole
4: a hole that goes all the way through is two holes.
The more energy a bullet has (ie, the faster it is going) the more energy the body absorbs in slowing that bullet down. The idea that fast bullets “go right through” causing less damage is plain wrong.
So, unlike D&D, there’s no magic number of hit-points a person can absorb, or any certain number of bullets which a person can survive.
In addition to previously mentioned reports of people surviving many hits with pistol ammunition, I’ve heard of a person surviving and recovering completely from a center-of-mass shot with a full-power battle rifle. I’ve also heard of a person dying from being shot with one .177 calibre pellet rifle.*
I am interested to know what prompted the original question. Can you explain?
~Wolfrick
*A teenage boy was being teased by neighborhood kids, when he was shot in the upper arm with a regular .177 caliber pellet rifle. The pellet entered a vein, was carried along by the blood flow, then lodged in his aorta, causing a blockage which was almost immediately fatal. Sorry, no cite.