2. The rounds are 2-3 times the size of .50cal. That means MUCH less ammo.
That was my thought, too. About 5 years ago I was working on a Navy contract mounting 30 and 40mm guns on Blackhawks. It put a large amount of stress on the mounts and frames.
The bigger gun isn't much of an advantage if you can only carry 200 rounds of ammo.
Doesn’t the UH-60 DAP (Direct Action Penetrator) have a 30mm option on the stub wings?