Why arenīt you considering the rate of fire?

On average 1 20mm hit is worth 3 50 cal hits. Some 20's are more or less, some 50 cals aren't so great, but that's the average.
That's probably why a plane with 6 50 cals is about firepower equivalent on a plane with 2 20mm's.

Read Tony Williams site and he does consider ROF and gives everything but external ballistics. The bottom line is how much mass the guns deliver per second, I guess explosives must be a special part of that.

In none of those does explosive 'power' play a major part. The in-game Ho-103 has explosive bullets with significant explosive.

Sorry you never blew a plane up with your 50's. You mustn't be hitting the right parts. An API to the fuel tank, often delivered in a massive waste of ammo usually does the trick.

With a P-47 and about a 2 and a half second burst from a 30-60 degree deflection shot you can potentially rip both wings off a 109. Maybe do the same to a FW190. Those are the tougher ones. The N1K2J seems crazy resistant actually but that plane is a bit weird DM wise sometimes. Everything else melts... at certain deflection angles the effect is even more magnified. Shooting dead 6 seems to produce the lesser result... likely because more bullets miss.

It all depends on aimed accuracy on target and your convergence distance.

I was a bit upset years ago after emptying a lot of ammo into the rear of a TU-2 (I think) engine nacelle and not even stopping the prop. When I posted about it, someone showed me a screenie of the TU-2 landing gear going up into the nacelle right behind the engine.

When a shot hits in IL-2 it spends its destruction on the first thing in the way. Until the thing in the way is destroyed it will stop shots. Only the skin and canopy, AFAIK, let a shot pass through. And from dead six there are usually a lot of parts to reduce before you get to something critical.

Shoot deflection and aim for the canopy, nose, wing roots. The parts up there pretty much all count right away.

Maybe use of same word "power" by Oleg and Williams with different meanings has caused some confusion: Oleg means HEI content whilst Williams means an index (that does include HEI content, if any) of projectile destructiveness.

Although we don't have Oleg's values for Ho-103, presumably it should be similarly destructive to real rounds, like the ones we have. Indeed, I can recall only one P-47 victory that I got disintegrating target by its eight Brownings, all the rest being "suffered" like if the .50 would be poorly effective, but now I agree it's mainly matter of aim. In addition, I guess minor dispersion of deck mounted ones help significantly.

Similarly, I had the experience of executing a Finnish G50 in this manner with the P-47 over Leningrad. But only one wing was enough.

A number of people had put in a lot of work over the guns, ammo and DM. They counted hits, they checked where the hits landed, they showed places where hits are worthless and they showed the good spots to hit. There's been small studies over online gunnery, do your hits count on the other end when there's lag? Sometimes they don't.

Dealing with wing guns, the magic word is convergence.

For determining where your hits land and how many, run and play back with arcade=1. It's amazing how few shots land sometimes.