Dang link gremilins.
http://boards.straightdope.com/ubb/Forum3/HTML/006192.html
[rant]
Speaking of Black Talons…
Did you ever wonder if there would be such an outcry against that round if it were named the “blue sparrow”? Definitely not. (did CNN ever run a story about the plague on society called the Hydra-Shok bullet? I rest my case)
I need to make a slight correction to what InutilisVisEst said about it: It’s not unfairly maligned. It’s VERY VERY VERY VERY VERY VERY unfairly maligned, for doing what a bullet is supposed to do. It is simply a slightly improved hollow point bullet with a dangerous sounding name.
And whose idea was it that a bullet can be “too dangerous”? Bullets are designed to kill. If you do not intend to kill somebody, then you damn well should not draw a firearm. Shooting at a person without intent to kill them does nothing but invite problems.
Police need a way to effectively dispense non-lethal force, for crowd control purposes, and because they live under a microscope where every decision they make is second- and third-guessed by the clueless masses and by politicians whose only concern is raising public outrage to help them get re-elected.
Civilians do not need non-lethal force from a firearm. If you discharge your weapon at a person and that person does not die, you will have much more trouble than if they had died. Unfortunately this is a flaw in the same legal system that penalizes a driver for avoiding an accident that, while not his fault, could have been avoided*.
But the bottom line is this: Bullets need to be fatal as often as possible, otherwise they are useless.
[/rant]
sigh
Anyway, to the OP, ideally, one well-placed shot should be all it takes. But when you are pushed to the point you need to draw your weapon, circumstances are already NOT ideal, by definition.
I assume the goal is to make sure you are out of immediate danger, i.e. Drop the attacker. Depending on where the shots fall (hopefully on center mass), what round is being used, and the mental, physical, & emotional states of the attacker, I would count on firing a MINIMUM of two shots as quickly as you can aim them, then appraising the situation again. If the assailant is enraged or on drugs, add one or two. If you’re using anything smaller than a .40 cal, add two more. if you’re using a .380, forget it and pick up a big rock. 
There are no dangerous weapons,
Only dangerous men.
Joe Cool
Look at the major controversy surrounding the Glaser Safety Bullet. A perfect home defense round - it would disintegrate and stay inside the house, instead of punching through three walls and killing the neighbors. But it became the evil ‘exploding bullet’, and sent the activists into apoplectic fits.
The rifling twist in the M16 rifle was changed because the bullet in standard NATO ammunition has changed. The slower twist, 1 turn in 12" or 14" IIRC, was sufficient for the older 55 grain bullet. The current 62 grain is much longer because of more metal, part of which is a less dense steel section in the front of the core. The tumbling on impact is a combination of the extremely fast 1:7" twist and the fact that the back half of the bullet is much heavier than the front. The newer bullet is also more prone to fragmenting on impact, causing further damage.
One of the infamous North Hollywood bank robbers was wounded by 29 bullets. In the lawsuit, presently in court now, a doctor testified that the robber would have survived if he had gotten prompt medical treatment (which was the basis of the lawsuit).
Even what appears to be a simple wound to the arm or leg can be a serious life threat. I have treated one girl that was shot in the upper arm with a .22 pistol. The round shattered her humerous, and tore her brachial artery in the process. We had to helicopter her out, she was bleeding faster than we could keep getting fluid into her.
Answer – 1 round, damn near anywhere between elbows to sholder, and from head to knees
Kinooning it up for 20 years and counting
slight amendment to last statement
1 round from… …can be fatal
Kinooning it up for 20 years and counting
Joe_Cool: Well said. I’ve had Talons as my primary 10mm load since they came out, simply because I liked their design philosophy (and they’ve been reliable). Among other things, their hollow point has a well to catch fur/clothing so that expansion in flesh is still possible. Be it man, wild boar or rabid dog, I expect my target to lie down and play dead moments after I pull the trigger. Why else would I bring lethal force to bear in the first place?
Glad someone brought up North Hollywood. Shot placement (head or neck) would’ve brought that situation to a conclusion much faster than number or type of rounds expended.
I think we’ve beat this to death (ha!). My take on it: rephrase the OP to ask “how many, what kind and where” and it quickly shows itself unanswerable.
I lead a boring life of relative unimportance. Really.
One of my favorite quotes from a book called “Survival Weapons”…
“The .25 caliber handgun should not be considered a realistic survival weapon but giving your opponent a faceful of bullets may allow you an advantage in the fistfight that follows.”
“Everybody smokes in hell”