In message ,
writes
What would be more effective for strafing -- An F-51 with it's six
50-calibers or an A-1 with its four 20 mm cannon?

20mm, definitely.

The .50 was a fine anti-fighter weapon for most of the war, blessed with
a good rate of fire, excellent ballistics, and reasonable lethality.
Against bombers it would have struggled, but the US rarely faced large,
armoured bombers. The RAF started with .303, rapidly found it wanting
and moved to the Hispano; the USAF had the .50 which was a good
all-rounder, even if with hindsight a change to 20mm for many roles
would have been better.

The USN switched to 20mm. the USAF didn't. Difference between Pacific
and Europe, perhaps?

--
When you have to kill a man, it costs nothing to be polite.
W S Churchill

Paul J. Adam MainBoxatjrwlynch[dot]demon{dot}co(.)uk