A pic of the flats would be interesting. Of course there are exceptions and the longarm could have been proved/reproved in 1910 but for the most part the 50,XXX range were manufactured from mid 1890s till at least 1900. Also on the "clock-hand" indicators is the term "Gesetz Geschutz" or registered design. This DRGM was #17913, I'll have to check the date, but it was in the early 1890s and I think it ran for 6 years, or more. It has the look of a "Knock-About" but with a Greener Crossbolt as mentioned and the tubes being weapons grade steel and the sculpted and engraved fences, it just may be a Deluxe version for the Contiental market. From time to time Vintage Sporting in Huntsville, Alabama,
http://www.vintagesporting.com/ - 256.534.9292 and he use to peddle longarms on GunAmerica, did have odd parts and I know he has had German receivers and tubes, but the site doesn't work and he may be out of business.
Kind Regards,
Raimey
rse