This value determines how efficiently an incoming round will penetrate your armor and how much armor damage will be applied to the inflicted armor piece.
value all refer to what is called the ammo penetration value. This term could also be called 'Flesh Damage'.
The term 'damage' on NFAM's ammo guide, linked at the very top of the page, refers to the amount of damage that is inflicted to your PMC when there is no armor to absorb or mitigate any damage from the round.
