I have a film somewhere (dont think our film viewer will show older films because it keeps crashing when I load old films) Anyhow, I was in a Ki-84, with less than 50rpg in my 12.7mm I shot off a tail of a P-47 that was bombing tanks, no 20mms and he had no damage, I just got closer then 200yards.
In an FSO event once I shot down 9 axis aircraft with 303s, all under 200 yards.
Thing is I tend to shoot under 400 yards, regardless - I wait and hold ammo otherwise I end up spraying endless for little damage. Most will joke the spitfire wings are "Weak" reality is it will take some damage, but in a turn fight the wings are exposed giving a big FAT target, little effort is needed to take a wing off when the target is that big, P51D however is much harder to hit on the wings if anything you take out a few guns.
Thus being said, Ive had a few fights in hurricanes where I dump half my ammo shooting at 400 or more, even in a P-47.
I think it comes down to distance, a 30mm can take a tail off with 1 hit at 1000k, problem is the size of the bullet it only needs ONE hit, a 12.7mm however disperses so much that you cannot get enough hits to do that kind of damage - so you end up spraying more ammo just to make up for it.