Marksmanship is not working as intended on armored Horses.

[Anabolic Man]

Weakspot hits does the same damage on an armored Horse as a Headshot without a weakspot. Weakspot Hits does currently not ignore the Horse Armor but only player Armors. I Personally think it should not only penertrate Armor but deal additional Damage on Pets aswell. A Skill to take out bears and horses a bit faster.

 

[Tzone]

It used to work but at a little bit reduced amount. IDK if it is currently not working because there is no reason to have MS except for PvE.
Mobs like bears do have a little bit of natural pierce resistance so MS does a little bit more against naked pets.

 

[Anabolic Man]

i did 57 normal damage and 57 Weakspot damage to an armored Horse so its not working for me.