The only AP round made for the AN/GAU-8 Avenger 30mm gun system is the PGU-14/B Armor Piercing Incendiary (API). That's the DU round. There is no "normal" AP made and the penetration for that round is reported in many places as being between 65-70 mm at 500 yards. As I said, we boosted it up a bit because attacks in the game happen at closer ranges than 500m so it was given a tweak upwards that it may not actually deserve.
Here's one source for the guns penetrative abilities....
GAU-8 Avenger
there are others
If you want to see an A10 light up a tank pick a target with less than 9 rear armour and attack from the rear. Most gulf war 1 Iraqi tanks qualify.
It's not a wonder weapon but it does have the mystique of one.
However, if I'm wrong I'm sure someone will correct me
Don