I think that was for non-combat situations. I don't think you should force pilots of P-51s to overhaul their own engines, too, while you're at it? Reloading was a combat limitation, barrel changes? Ehhh.. not so much.
P.S. The ammo boxes contained 20 rounds only. You could fire all 4 guns but only for 20 rounds. In WW2 they didn't spray nonstop streams at planes like they do here. They also weren't so invisible as they are in here.
IMO the wirble needs a heavy perk. Then they need to introduce the 4x20mm flak halftrack. Same gun but open turret, minimal armor. Even MGs could take it out. THAT and the M16 should be unperked.. possible leave the Osty unperked as an inbetween step from the halftracks to the Wirb. Maybe?
THIS is what Aces High should have modeled instead of the wirble: The SdfKz 7.
It was THE workhorse of the German army. Over 5000 produced and saw service in every part of the war. Loaded out in many quite common variants, it carried a 37mm like the ostwind:
(note those sides on the flatbed are laid flat for operational use)
It towed 88mm:
It had quad 20mm like our wirb:
If we had the firepower with a much softer (and let's be honest, more representative) target, it would be a better tradeoff. Then the armored tank-chassis osty and wirb could be perked.