I'll spawn another TTK thread, even though I really mean this to be a buff the armor in a balanced way thread.
I think everything should OSK on headshot.
I think rifle and sniper rounds should OSK to the chest (unarmored).
EDIT: and larger pistol rounds for unarmored targets (thx @GSG_9_LIGHTNING)
I also think armor should actually be useful.
Instagib through armor:
(1) Isn't fun
(2) Increases the pace of the game and makes it less tactical
(3) Lowers the skill ceiling
Reasons for my above observations are everywhere in every TTK thread, I won't restate them.
(1) Should be cheap
(2) Should only affect pistol rounds and like the UZI (smaller calibers)
(3) Rifle and sniper rounds should ignore it
(4) Should barely impede movement
(1) Should be more expensive
(2) Should take significant torso shots from rifles (that aren't sniper rifles, aka high velocity) using 7.62 NATO, 7.62x39, .40, .45 ACP, .357 SIG, every pistol caliber
(3) 5.56 should (realistically) ignore it... I'd be happy if it was just better at penetrating than the above calibers
(4) Sniper rounds should ignore it
(5) Should significantly impair movement
AP ammo is unnecessary, considering snipers should bypass armor completely, 5.56 should bypass armor, and certain firearms in game use AP rounds by default (MP7).
In his post @Zayzek said "pistols are useless because they need about 4 hits and the bolt action snipers can't kill a heavy armor in one hit, the weapons should always have AP rounds on them, Insurgency2 was fun because of the 1 hit kills."
Above I've addressed every point.
I reiterate, OSK/OHK/instagib lasering people isn't fun. I liked Ins2, but I had problems with it. I like Sandstorm better.