ISP sums it up quite well, and helps explain the varied anecdotes. Much depends on distance and shot size. Up close, any size shot will work fairly well, the farther away you get the less likely it is to work.I don't recommend birdshot for self defense but don't minimize the effect and devastation it can cause at normal room sizes. It's very deadly. The downside to using birdshot for defense is it loses it's velocity quickly.
My cousin was shot three times with 00 buck from less than 50 yds. He was badly hurt but recovered. Nothing is 100%.
Being able to reach those organs is one thing. Being able to cause enough damage to incapacitate an attacker is another thing. Just pointing that out.Ask any paramedic, the lungs are easily reached with a 3" needle, less than 5 to the heart.
Since many of you have apparently not shot a shotgun, I can tell you this:
A magnum load of 12 ga. BB shot at close (HD) range will blow a large hole very nearly through a man. "But-what about the FBI's recommended 12" of penetration? What if his arm is in the way?"
He won't have an arm-at least much of one, anyway-and there will be a large, deep hole behind what is left of his arm.
I find it comical that people can not comprehend this!
If, for some miraculous reason a shot like this did not instantaneously render an attacker immobile, I can guarantee he will be going in the other direction-not towards you.
And I've posted before I had a high school friend who got half his head blown off from bird shot, or enough of it he lived on life support for only 3 hours. Until I see something different in RL which contradicts that experience I'll keep to my own opinions before being swayed by folks on an internet forum, no matter how well intentioned they believe they are. Sorry, seen the results first hand.
Birdshot is for birds.