no sane man will use JHP against armored target. You use AP and then the DT is divided by 5. case here is that with BA and 2x toughness you have 12 DT (11 probably due to fast droping DT on armor when detettiorated) stil lthe value divided by 5 so its 2 against 1 if you have just one toughness - this one does alot of differance.in case of metal armor it substacts one with and without second toughness so its just the 5% DR extra
http://fodev.net/forum/index.php?topic=1129.0
"Armor piercing" property works like giving the weapon free Penetrate perk
Penetrate perk is weapon's feature, not ammo's. Thats what I can see in words
Ammo got piercing perk that does exactly same thing as penetrate on weapon. ask solar if you dont belive me.