I wouldn't say anything about cannon damage based on documentary films. The footage is gathered from here and there and there is no knowing what the original context was i.e. what aircraft was hitting what and with what weapons.
Eg. there is a much used clip where a FW190 loses half of its wing allegedly from a .50 Cal hit. It is indeed possible that it was hit by a .50 Cal, but that is not the usual effect of that gun hitting an aircraft, unless it hits the wing ammo compartment which it probably did in that clip (there is a good reason why the "Sturmbocks" had heavy armor in their wing mounted 30mm ammo boxes). The effect would be pretty specatcular too if the wing root gun compartment in 190 was hit, cooking off the ammo in fuselage ammo compartment.
The british film is legit as it is clearly part of an official test documentation. Too bad there was not a clip of the Hunter's 4x30mm hits...
-C+
