Yesterday I chewed off both wings, all stabs and some bonus extra from B-17 in one single pass with P-51, used up total of 250 rpgs from all guns.
Doesn't sound like this would really happen, thats like perhaps 80 rpg into both wings, 50 rpg into tail and rest bullets into fuselage.
Again, when I shot B-17 with 3*20mm + 2*13mm, I did use very much ammo just to chew off right wing only.
Both times made same kind of attack with same type of convergence settings.
Now I am wondering, is those .50 caliber guns upgraded too much, I agree that they were lousy in 0.36, but now they are like zipped death star. (hmm, haven't tested .303s yet in 0.37)