I am once again guilty of picking up strays. Just found a hammer drilling in need of some major help, which this time will include welding.
Aside from that and pictures later, it is an Austrian double 20 (15.1 on shotgun over an 11.7 stamp on the rifle) which could be a mystery Werndl type round.
It has both Austrian (EF) and German (crown G and Crown S ) stamps on the respective barrels.

The number string on the bottom rib is: 4022.09.150 15.1 11.7

Maker is M. Ogris Ferlach.

Thanks

Tom

Carbonation without fermentation is tyranny