yeah, i mean, 3-4 rounds of 20mm would break a fighter apart, may 5-10 far a bomber. As for the inf, there should be something like a small flak burst, like on the 40mm and 88mm, but right now they are just bullets. THis also makes it hard to hit a plane with that 20mm aa gun.
Actually, U.S. fighters were surprisingly well built and sturdy. A 20mm HE round was reported to put a "baseball-sized hole" in a fighter or bomber. It would take 10 or so rounds to down a fighter and a lot more for bombers, depending on where you hit. That's part of the reason the 30mm rounds were developed. Those put a swimming-pool sized hole in most things, including bombers.
Yeah, but for a good pilot, like me, I would put m cannon rounds all in one place, like a wing root. 2-4 there on a fighter, along with the MG fire, he is history.