Since things are quite Dead herein, Wolfgang & I have had an offline interesting discussion on the number of Fünflings out there???
Ferlach Fünfling from the 1970s coming in @ 10 kilos, chambered in a triple of 10.2mm and one 0.577" for some fella in the U.S. of A. that had one hell of a Porter or Gun Bearer. Parts were machined at the Ferlach Consortium and then Gottfired Juch cobbled it all together, stocked it and sent it thru the Ferlach Proof facility.
Then there is another one on Reddit:
Might any of our Merry Band be the custodian of one?