Talk:Damage 1.0/Armor Piercing Damage/@comment-17579027-20130903133109/@comment-10743657-20130919154600

It's effective against both. Corpus take 2x damage from AP on headshots, stacking on the 2x you already get on headshots, so you get 4x total damage.

Only medium Grineer take extra damage against AP, and it's 1.5x.