Recently, while I was doing some research for a hunting column that I was writing, I came across these two quotes from Finn Aagaard. Now, of course, Finn was talking about hunting, not gunfighting, but I realized that they are just as important to the defensive shooter as they are to the guy out collecting his venison.
We are fortunate that we live in a time when there are so many well designed defensive bullets available to us. I'm old enough to remember the time when that certainly was not the case. In order to stop a violent attack quickly, the bullet must penetrate adequately and it must expand in order to impact the greatest amount of tissue. Unlike the hunter, we are not trying to cause death—we are trying to cause an immediate stop to a violent criminal attack. But the principle of bullet performance is the same.
However, even if we have good ammo and great bullets, we must place the shot so that it will stop things immediately. Some people use the term "center of mass" to denote the spot to place the bullet, but I don't like that term. A person's center of mass may be, and probably is, continually changing. It is far better to think of placing the defensive bullet in the "vital zone." That is the area of the upper body where the bullet has a chance to impact heart, lungs, major arteries and the spine. The destruction of this tissue, as Aagaard points out, will cause the body to stop functioning and the bad guy will cease being a threat.
So, buy whatever cheap ammo is available for your practice sessions; that's okay. But buy the best quality defensive ammunition for carry. And, oh yes, I think I've said it before, but.....practice, practice, practice.