[grvreijn]

I´m not the specialist on this but tracers were definitily used. Including on 20mm. Many original guncam fims exist on which clearly tracers can be spotted.

1. I think I read somewhere RAF added additional tracers or only tracers in the last 10-20 rounds indicating to the pilot he was running out of ammo. The rest of the amo also did contain tracers.

2 20mm definitly also had tracers. Not sure about larger types of ammo.

3. I was not around in WW2 but was a infantery MGunner much later. With us every 5th round was a tracer. A tracer is glowing all the time otherwise it does not serve its need.

I´m convinced flex mounted guns also used tracers. I agree that it would otherwise be impossible or pure luck for a waist-gunner to hit a passing enemy fighter.