The mechanics for hit boxes in Gunz are not very complicated. There are only two hit boxes, each dealing different damage percentages to HP and AP. When there is no AP remaining, 100% of the wepaon's damge is taken away from HP.
On the diagram, area 1 on super cool Aqua Man represents the headshot range, which deals 75% of the weapon's damage to HP, and 25% to AP. Headshots are preferable for this reason, since lowering your enemy's HP is the primary goal.
Area 2 represents body shots, which deal 50% of the weapon's damage to HP and 50% to AP. Body shots are not as effective as headshots, but easier to accomplish.
Armor points add up for a total score. The location of the armor is not important. For instance, someone wearing 10 AP boots and nothing else has the same exact armor effect as someone who wears 10 AP chest armor, no matter where the person is shot.
1. Hits to the very upper chest + head deliver 75% of the damage to HP and 25% of the damage to AP.
2. Hits to the lower chest and below deliver 50% of the damage to HP and 50% of the damage to AP.
3. If the damage equates out to an odd number, health takes the lower amount and the extra point is taken away from armor.
4. Armor Points are global. It doesnt matter which armor pieces you're wearing, only the total number of points. Not wearing armor over a peice of the body does not effect that part of the body more or less than any other.
5. If you run out of AP, 100% of the weapon's damage is taken away from your HP.