Bought this shell & casing quite some years ago. One of my first items i bought in fact.
Its an 88cm Flak casing & projectile
The casing is in steel I believe. And the projectile is painted green/grayish with black bottom and red/brow top (looks quite rusty in the picture). The inside is flat white.
Dont know much about it but according to a local military historian the casing is marked as fired once (see pic - circled).
What does the other markings mean?