your headstamp is not common but it clearly “regular” (on mine the “smi” is light stamped)
i had a similar round with german marquings and a small “smi” on headstamp (there are the first lot with lacquered reddish/brown steel case go to italians
headstamp: eej 42 17d smi
To be honest it is not really German in style. But that may be secondary.
I am just not getting the stainless steel part here.
I’m not well versed on this but I can provide a little info.
Your 20x138mmB case is a product of Bombrini Parodi-Delfino, 1943, lot 759. No ‘L’ in front of the lot number may indicate this was produced for the Italian Army as production for the Navy had an ‘L’ before the lot #. I think ‘15 VII - 41’ is loading information. The case appears to be STEEL, with a phosphate/Boderized surface and a lacquer type finish, typical of WW2 production. The projectile obviously has a nose fuze and is probably a loading for antiaircraft use, but since much of the color coding appears to be missing (or I just can’t make it out) it is hard to say what type of loading the projectile was. Nice clean round/headstamp.
If this is incorrect or if someone has better info don’t hesitate to jump in on this.
Thank you, and sorry for “stainless” part, my mistake. I work in the bio-pharmaceutical industry, where all steel is stainless, so it is a reflex, when I think “steel”, I write “stainless”.