A mysterious 2 cm FlaK 30/38 shell casing

Hello everyone !
A very recently I have received what I believe is a 20x138 B (solothurn long) shell casing intended for usage with FlaK 30/38 anti-aircraft gun. There is something very strange with this cartridge - its bottom markings. No proof marks, no waffenamt, no other symbols or manufacturer logos - just numbers.

I will post photos of course but in case the picture of the bottom is not visible enough for you here is what is stamped there. On the left side there is a number 25, on the right side there is a number 51 and in the upper section of the bottom there is number 100. And that is all my friends no other symbols or logos - like I said.

Now, Iam well aware of the fact that there are not only german examples of this cartridge but also Italian, Swiss, Dutch, Finnish, Greek, Hungarian, Czechoslovakian (after ww2) equivalents as well as various drill or blind rounds and I have studied them. No luck for me so far. I suspect that the number 51 might be a date of production - 1951 but I am really just guessing.

Most similar to my casing was Swiss example but they shared only one number and the Swiss one also had other markings while mine has none. So my questions are where was this casing produced (country), by who (company/plant) and in which year ? Also the meaning of the aforementioned numbers (if not corelated with my previous question-(25 , 51, 100).

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