Just found this. Was checking it out in Kent’s book (pg. 53) and it doesn’t show this year but it does have nice paint.
What you have is a 7,92x57 PmK ( phosphor - ap ) round.
Made by Polte Magdeburg Lot 88 1937.
Just a side info as we have a thread running in parallel with .303 smoke tracers:
This one here is as per British designation an “AP smoke tracer” as the white phosphorous filler is ignited the same way as in the British rounds.
The German “PmK” stands for: “Phosphor mit Kern” (phosphorous with core).