I was looking at ammo types I have while at home on lunch (LOL, addict) and I noticed that some have +enemy DT. Why would you want to add to your enemy's damage threshhold? Or am I just reading it wrong? I had another kind that have a minus to damage reduction, which seems like it would be useful... Again sorry for the noob questions! -Meg

HP, hollow points. likely what adds DT, but does x1.75 damage.
JHP X.95 damage. Looses some damage but does not hinder under armor.

AP Armor piercing .95 damage Targets DT -X.XX I think the .50 is damage .95 but target DT -15.00

The trick is Hollow Points multiply the enemies DT. So if they have no DT it does nothing. They also have more damage than a regular bullet. Therefor, on an unarmored target, it's going to do more damage than a normal bullet.

AP bullets do less damage, but reduce DT. So a target without any DT would take less damage from them, but on a higher DT target they come out ahead.

Use the ammo types with DT multiplication against enemies with zero or very low DT, then the damage multiplier allows you to do high damage against them. It's meant to simulate hollow point bullets either shredding flesh or splintering against armor.
Bullets with DT reduction have lower base damage, which means that against zero or very low DT enemies they do less damage than regular ammo, but against heavily armored targets the DR reduction means a larger part of the base damage goes through. Simulates a solid bullet piercing a neat hole to flesh or going through armor and then piercing a neat hole through flesh.

Ahh ok, thanks. I feel like I should go to "gun school" or something