...developed because the FBI's limpwrist brigade couldn't consistently qualify with a Man's cartridge.
The original 10mm loading was never issued to FBI agents, so problems with qualification never had a chance to develop. They settled on the downloaded 10mm before ever issuing guns or ammunition.
In your opinion, what is the % chance that just 1 shot from .40, through the heart, with THIS SPECIFIC ammo and sized gun, will do the job? No matter how big the person is.
Instant incapacitation? Probably not. Incapacitated within a few seconds? Probably.
Depends on where the hole is. Straight through the middle--good chance. Straight through the top--better chance. Through the arteries at the top--really good chance. A small hole at the bottom? Survivable--ask Stacey Lim.
Do you know where the heart is? Not on a 2D target viewed from the front, but inside a 3D target, viewed from any angle?
Can you hit a target the size of the heart on a moving target?
Can you hit a target the size of the heart while you are moving?
Can you do all that while you are being shot at, possibly after being wounded yourself?
The fact is that during a dynamic encounter, the point of impact can not be tightly controlled. In fact, it's common for more shots to miss the attacker entirely than score any kind of a hit, let alone a perfect heart shot.
Is one lung being taken out lethal...
Lethality isn't really the point of self-defense. The practical point of self-defense is stopping the attack. It does you no good if the attacker dies 15 minutes after killing you, nor is it a bad thing if the attack stops immediately but the attacker survives.
Second, shooting someone in a lung will probably incapacitate them eventually and may be fatal, but it's not likely to happen quickly.
1. Pick a quality gun that fits you, that you will carry, that you shoot well and in a common "service pistol caliber".
2. Practice a lot with it. Shoot it with both hands, one hand, one hand weak side. Practice clearance drills. Shoot it when you are tired. Shoot it on the move. If you can find a place that has moving targets, shoot at some moving targets. Practice in low light. If you can find a place that lets you shoot from unorthodox positions, do that. Practice drawing from your carry rig. Watch some real-world shooting videos and see what causes people problems in the real world, what works and what gets people killed. Get some anatomy training so you can visualize the internal structures of the human body from various angles. Get some physiology training so you understand what parts of the body are likely to result in incapacitation if damaged.
3. Pick premium self-defense ammunition from a major ammunition company with an excellent reputation for quality and make sure it works perfectly in your gun.
4. Learn about the laws of self-defense and the practicalities of it.
