1. Disrupt central nervous system.
Just striking a suitable blow to the CNS can result in a person going down.
That is how the boxer's punch works.
You know how it feels when you bump the nerve in your arm ('the funny bone')?
Imagine that same thing in your brain.
A blow can cause the nerves to spontaneously depolarize ('fire') resulting in recovery time and the temporary inability to control whatever those nerves control.
2. Shatter a supporting bone structure (pelvis, femur, etc)
Not likely with most handgun calibers except the vary largest.
And the targets are small and not always easily located with ebough precession from a distance.
3. Exsanguinate the target (bleeding out).
Could be just a few seconds to minutes to hours depending on how big a bleed you create.
Blow the heart, hit the aorta, major pulmonary circulation, etc. the person will be down very quickly.
If they make it a full minute they are doing very well.
Hit a femoral artery and they might last a few minutes if the wound bleeds freely (no tamponade effect from the surrounding tissue).
Smaller bleeds take longer.
Killing quickly is not a simple matter with a handgun.
Compared to most rifles they are far lower power and simply cannot create the often massive destruction of a rifle bullet at much higher speed.
Head wounds that may not prove lethal if you are close to care can be very lethal if they disrupt breathing.
It take a lot of muscle coordination to breath, and it can be disrupted by damage that does not appear that significant.
Breathing support after head trauma is a relatively knew thing.
For a long time it was assumed if you stopped breathing as a result of head trauma you were as good as dead.
The army finally figured out that breathing may stop, but can resume of pulmonary support is provided to avoid brain death.
