"Ctenos" (reply w/o spam) wrote in message
...
Is there a consistent basis for this designation in aircraft armament?

All cannons *are* guns, so it is OK to refer to them as such; but all guns
are not cannons. I'd imagine (educated guess only) the division between the
two comes at the point where typical loads can include "payload carrying"
rounds, which is at the 20mm point (not aware of any *typical* loading of HE
into rounds under that size, which is why the 14.5mm is still refered to as
a machine gun and not a cannon).

Brooks