I suspect Robert Schüler of Kòln possibly was more of a firearms merchant than anything else seeing he peddled higher end DRs, vierlings, etc. and there seems to be so little info on him so how could he have such a shop and a group of craftsmen to produce the examples he peddled. Well, it seems he couldn't and sourced from his relatives/cousins and others in Suhl.
Here's the 600 Nitro clamshell that Monty Whitley had at the 2009 Vintagers which I think is still on GunsInternational. It is a handful at over 15 pounds, and about $3500 U.S. of A. per pound if I recall correctly, and more than likely requires a gun bearer shoulder for shooting assistance.



Kind Regards,
Raimey
rse