From what I understand, armor piercing ammo applies a modifier to the Determining Critical Hits Table, i.e., AC/20 is -1. What happens if I shoot AP ammo and I roll for a location getting a 2 on hit location table? Rules say I roll for critical hits but the AP ammo already does a critical hit. Do I roll twice on the Determining Critical Hits Table or once if I roll a 2 on hit location table? Do I apply the AP modifier once or both times if I struck an internal structure location that isn't armored?