Mostly directed to Zerg - the aircraft weapon damages vs aircraft were already fairly precisely set, based on the second table on the page here (the “gun power” value). Feel free to scale beyond that, but those should probably be the base for how various guns relate to one another.
Ah, interesting. I only took HE filler weight into account in my own consideration. Somehow the MK108 ended up with less damage than the MG151 before my change; I’m investigating how this came to be (may have been caused by the damagetype script).
Energy Scores, further down the page:
.303 Browning (7.7x56R, incendiary): 0.25
.50 Browning M2 (12.7x99, armor-piercing incendiary): 1.73
15mm MG 151 (15x96, high explosive): 1.92
20mm MG 151/20 (20x82, armor-piercing incendiary): 2.32
20mm MG 151/20 (20x82, high explosive mine shell): 6.53
20mm Hispano-Suiza HS.404 (20x110, high explosive): 4.86
20mm ShVAK (20x99R, high explosive incendiary): 2.82
23mm VYa-23 (23x152B, high explosive): 7.13
30mm MK 108 (30x90RB, high explosive mine shell): 23.03
Apparently it took about 4 hits from the 20mm MG 151 to down a fighter -> ~60-70 damage versus planes. I would guess this is from the mine shell variety, with about 20 g explosive. At the tentative standard of 2000 damage per kg of explosive this would be 40 damage from explosive alone.
Do any of our current aircraft use the 0.303 or similar weapons at all? I know the GAZ-AAA anti-air vehicle is armed with 4x7.62 MG, and that’s probably the only rifle-caliber weapon likely to hit planes?
As for HE vs AP shells, I’d expect HE to be less effective against armored planes like Il-2 or Hs.129 (which is modeled, but not included). But that aspect is probably not worth the effort to implement.
Hmm, I guess not; I must have been thinking of the earlier Spitfire models.