Talk:Vectis/@comment-16584725-20131031111131/@comment-10114595-20131031162848

AP does straight up double damage to Corpus heads and 50% more to Grineer bodies, that's why. You're getting 120% effectiveness for the former and 90% for the latter.

Other damage types also have armor applied to them, AP if I recall right is in the same boat as Physics Impact...no armor calculations applied. Add more AP, you add more effectively armor-ignoring damage. It doesn't matter if the weapon is inherently AP, Piercing Hit will still apply extra in a separate packet (as with any other elemental mod).