"Armor Piercing" means that any Armor Rating counts as half against this weapon, rounding fractions up.
I noticed that in Foundry VTT this is rounding down. You can test and confirm this by using any armor that has an odd number for its Armor Rating.
Example: a Hazmat Suit, which has an Armor of 1. If you try to do Armor Piercing on it, it ends up saying you have no dice to roll, but according to the rules, you would still get your 1 armor.
Page 118 of the Core Rule Book states:
I noticed that in Foundry VTT this is rounding down. You can test and confirm this by using any armor that has an odd number for its Armor Rating.
Example: a Hazmat Suit, which has an Armor of 1. If you try to do Armor Piercing on it, it ends up saying you have no dice to roll, but according to the rules, you would still get your 1 armor.