what we know: is it a real 10mm /400 and it have a paper thin neck
there are very few 10mm cartridges in germany/austria. beside of the 10x60R 400 only some 10 mm target rounds bases on the 11,15 x60R mauser brass. there are maybe also other wildcats from this time I did not know but...
the paper thin brass case is typical for the early express rounds and the 10x60 R 400 comes from one. this is not a 450 basic case necked down. the 10,3x60R swiss is such a thing.
ok, the camber seems to be to short for a 60 mm long case but maybe it fits. old chambers are made different than we do it now. I have casting were the chamber ends with the case mouth. no free bore, nothing, the lead bullet engrave into the rifling when loaded.
I can only tell you what I would do: talking with cartridge collector for getting an original 10x60R 400 from Georg Roth and try to load it. I dont know if this is a problem for you, can only tell you that I would get it here in some days.
the 10x60R 400 was the only standard factory 10 mm cartridge and it was popular around the turn of the century
franz sodia ferlach
georg roth 1927
original bullet weight was around 250 grains. i think you will find something for the 10 mm auto