I'm in violent agreement with
Scrubcedar in that
what you hit is more important than the size of the projectile.
You have to hit your target to be effective.
You also have to hit some crucial or
vital structure to stop a threat.
Any bullet that can penetrate to the far side of the body can be quickly lethal.
Realism 101 - My perspective
I'm a good shot. But I'm old and rusty and no longer competing in matches. But I'm still a good shot but by no means an "expert" shot. While I can make COM shots on paper, I know my skills and accuracy will suffer when I have to try to shoot a real, moving target. And they'll suffer even more if that target is
trying to kill me. I know all this.
Still, I want the threat to end as quickly as possible. Ideally with one bullet. My aim isn't going to be perfect. My form will probably look silly as I'm trying to not be killed and screaming like a girl. Since I won't be able to place the shot with precision, bigger bullets are better. Bigger bullets mean bigger holes. That means an increased chance of damaging something important. Say, his
descending aorta. Or
inferior vena cava. A big bullet doesn't
need to expand, but if it does it's just that much better. Bigger holes mean faster blood loss. That means I may not have to shoot him twice. Or four times.
I'd much rather have the cops looking at my downed assailant who has one hole in him rather than two - or four, or even seven. If the assailant dies, I'd rather the doctors tell police it was fatal because of
where he was hit rather than the number of times he was hit.
If you shoot your best with a .380 or 9mm, then using it will probably serve you better than trying to use something bigger that you shoot less accurately.