Hi Silo,
>If a Browning AP round hit a wing, and a Breda HE round hit a wing, would the Breda HE round make a slightly bigger hole on the surface?
Excellent question! :-)
The amount of explosive contained in the Breda shell was so small that it must have been fused to explode immediately on impact to do any noticable damage.
Let's assume all rounds hit a sheet of metal at a 90 degree angle. I'd expect these results:
Browning AP: Small hole.
Breda HE: Slightly larger hole with damage at the edges
20 mm AP: Slightly larger hole.
20 mm HE: Irregular hole, skin buckled
20 mm Mine: Slightly larger irregular hole, skin buckled.
Now let's assume a second sheet of metal is arranged 20 cm behind the first one. What would the damage to the second sheet look like?
Browning AP: Small irregular exit hole.
Breda HE: Some fragment damage, buckles, small irregular exit hole
20 mm AP: Slightly larger exit hole.
20 mm HE: Large area with fragment damage/buckling, perhaps small fragment exit holes
20 mm Mine: Large area buckled
(The buckling of the aluminium skin has a similar effect as tearing a hole into it as it's unable to carry loads in that condition.)
Next, let's see what happens if the two metal sheets are two surfaces of a small metal box, affixed by rivets, simulating the confined volume of an airframe's interior construction:
Browning AP: As before
Breda HE: As before
20 mm AP: As before
20 mm HE: Much larger ingress hole than before, skin torn and bent outwards, larger area of skin buckled
20 mm Mine: Even larger ingress hole, skin torn and bent outwards, edges of the metal sheet torn off the rivetting in some places.
(Boxes like these were actually used for ballistic trials in WW2.)
In short, the filling of the Breda HE projectile is too small to gain similar benefits as from 20 mm HE or mine shell rounds. Its destructiveness against the unprotected aircraft wing is probably similar as the Browning's, though the latter's higher kinetic energy might cause larger damage when it can be converted to damge fully, for example by striking a structural member of the airframe.
However, heavy machine guns (and even 20 mm AP rounds) weren't really effective against the wings of WW2 aircraft anyway - they were designed to attack critical components and could only achieve crippling airframe damage if a high number of hits was scored.
By contrast, 20 mm HE and mine shells were easily capable of destroying the airframe without hitting any critical components. The mine shells were designed to be much more effective than normal HE shells: Since they carried a much larger explosive charge, they could rip the aircraft skin off the rivets, creating a much more serious by weakening several cells of an aircraft's wing where a normal HE round would only have affected a single one.
This discussion of airframe damage is much simplified, of course, and the damage I described is an estimate based on what I've read on this topic. Don't take it as the last word, though I'm quite confident that my descriptions are fairly realistic :-)
Regards,
Henning (HoHun)
