Talk:Kunai/@comment-80.2.188.209-20130709204434/@comment-10743657-20130710151038

Here's a more thorough answer:

Kunais deal a type of damage (Physics Impact) that are on the armor ignore list for most enemies (there are exceptions). Armor piercing is another type of damage, just like Fire, Poison or Bullet. So adding AP on will allow you to deal more damage, especially to armored targets because they, medium Grineer that is, take 1.5x from AP.