Already put in my few grains of salt. Originally this was a standard Tell II in .22 short rimfire. Later, but still before 1912, it was rebored, rerifled and reproofed to take some 8mm or .32 cartridge.If it is still a rimfire, there are only the possibilities .32 short or long rimfires, shown too in the German 1908 Akah catalog but called .320 in Europe. According to COTW these cartridges are long obsolete. Some ammo was imported from Brazil to the USA about 1990. If converted to centerfire, the most likely options are .32-20 Winchester, 8.15x46R or 8x48R S&S. The .32 Winchester Special and the .32-40 were unknown then in Germany.