marauder2048 said:
I hate to be blunt but it's pretty feeble analysis which falls far below the standards of the detailed Ballistic Research Laboratories reports of the mid-to-late 1940's! They actually looked at things like drag co-efficients, retained energy, fragmentation, yaw, HEI composition and its effects on fuel tanks and aircraft structure. And they had the huge advantage of performing their analyses with live rounds.
My analysis might not meet your high technical standards, but it does have the benefit of producing realistic results consistent with combat experience.
And in fact the Soviets actually shifted from 37mm armed P-39s and 23mm armed Yaks to 20mm armed Lavochkins.
Which probably tells you a lot more about the characteristics of the aircraft than it does the armament. And they still stayed with cannon, they didn't move back to HMGs.
And if you look you'll find cannon on US aircraft in theatres (the Pacific) and operating environments (e.g. a night-fighter like the P-61) precisely where there was a heavy aircraft threat.
Depends on how you define "heavy" - and "well-protected" comes into it as well, something which Japanese planes were not noted for until late in the conflict.
To sum up, a quote from the second article I linked to:
To return to the original question, were the Americans right to rely so heavily on the .50 M2 when all other combatant nations had a clear preference for cannon of at least 20 mm calibre? The answer has to be yes. It was adequate for its purpose, and was the only satisfactory aircraft gun in production in the USA. It was very reliable (except where the installations created problems), was made in huge quantities, and the simplification of supply by comparison with the diversity of weapons used by the Axis powers gave a major logistical advantage. However, the Americans could get away with using a weapon so deficient in destructive power not only because of the nature of their opposition, but also because the size and engine power of their fighters enabled them to carry a battery of at least six guns, thus making up in quantity what they lacked in destructive quality.