http://www.ratical.org/radiation/vzajic/3rdchapter.html
(" For example, 30 mm DU rounds from GAU-8A automatic cannon mounted on A-10 Warthog aircraft can pierce steel armor up to 9 cm (3.5 in.) thick."
Here's an interesting fact... PGU-14 API DU bullets, not the entire cartridge, weigh 298 grams. If you look at the weapons table in FC2, you'll notice all of the rounds are given the exact same mass.
Another interesting fact: Right after I posted this, the thread was moved to the far less seen Mod section. Yep, the hazards of being the canary in the coal mine.
That's pretty heavy High Explosive, isn't it?