The cartridge is likely 12.7x60R / .500 Express (Short); a popular black powder hunting round in Austria-Hungary at the turn of the century.

This seems to be a pertinent Georg Roth case from 1897: https://one.nbstatic.fr/uploaded/20170205/3676800/thumbs/450h300f_00001_RARE-12-7-60-R-D-Express.JPG

And another reference: http://old.municion.org/12_7/12_7x60R.htm

Sigott was one of the leading Ferlach makers at the time. Nice catch.

Kind regards,
Jani