Hi @fert,
I just had another look at your very nice and interesting round. It's not often that one gets to see a specimen in such a perfect condition. The casing is stamped "P" for Polte. One would expect a company like Polte to be working on developing 20mm ammunition. What surprises me, is that the electric primer is not stamped at all. As far as I know Polte did not produce electric primers. The only manufacturer, that I know, is Rheinmetall-Breslau. They invented the bridgewire cap. There were discussions, in military circles, at the time, for their synchronised use for ever faster fighterplanepropellers, so the pilot could shoot straight ahead.
Many specialists at the time thought, that it was not possible to heat up a bridgewire precisely in such an extremely small timeframe. Rh proofed that it is possible. Does anyone know of another manufacturer of electric priming-caps for cartridges, at that time, in Germany ?
Regards,
Bellifortis.