I have had for some time these 2 cases in very bad condition. Maybe somebody on this forum has more information?

The long case is more "common", I have seen several examples. According an acknowledged collector they are 12,5 mm and found on experimental ranges.
The shorter case I have only seen my example, it is supposed to be a Czech 13 mm AT experiment.

Dimensions (for as far as they are accurate with these damaged cases):

12,5x165R22
13,0x133R22

Of course no head stamp, that would make life way to easy ;-).

Ciao, the case on the right is corroded. It seems to have been underground, do you know the place where it was unearthed?

Not 100 % sure. Apparantly the 12,5 mm cases are all found on a well known German range (do no remember which one). I have no information on the 13 mm except that the seller told me it was a 13 mm Czech.

here doc for 12x165

regards

Thanks! I also got a copy of the original Czech drawing for the 12 mm case (and an unknown 15 mm) thanks to DJ.

I think also this, is part of the same project:
7,92x145

Interessante la soluzione del bossolo bimetallico su una lunghezza simile
Il terzo è bimetallico con alluminio?
Ps: la canna soffiava ancora dopo 10 minuti che la palla aveva impattato

Con una canna di quella lunghezza e le velocità che volevano ottenere il proiettile per l'attrito fuoriusciva al calor bianco, praticamente non avevano necessità di tracciante!

And I received another set of 2 drawings from DJ.