Back in The Before Time, we would practice failsafe drills… two to the body, one to the head. We also practiced hitting the ‘pelvic girdle’. In other words, when a bad guy is wearing body armor, shooting him center mass is only going to piss him off.
But if you hit him a couple times in the pelvis, he is going to go down. Body armor does not cover the pelvis (unless the bad guy is wearing a bomb disposal suit), and hitting a bad guy in the pelvis or hip joints with a couple high-velocity well aimed shots will shatter the bones, rendering him prone and pretty much out of the fight. If your aim is off and you end up shooting him in the junk, well.. he shouldn’t have been messing with you anyways..
Armor is also vulnerable at the neck and shoulders, especially to oblique or side-on shots.
ANY part you can see of your opponent is fair game. If all you can see is his foot, then shoot him in the foot. Might not put him totally out of the fight, but it will cripple him and cause his aim to be off… often, bad guys would take cover behind vehicles. Which works only so long as your opponent doesn’t realize that he can bounce bullets under the vehicle. The bullets hit the pavement and fragment, the wound patterns resembling a shotgun wound. It is effective.
The wicked flee when none pursueth..." - Proverbs 28:1