someone build a sizing die to make shells for the 0,70" Randschlussspiegel cartridge from 20 ga plastic, notice the step over the rim http://egun.de/market/item.php?id=6087006

.22 patent rifle with later made threads on the muzzle, suspect for a silencer what was common before WW 1, no proof so before 1893 and SN not found
http://www.gunvaluesboard.com/fv-dreyse-22-cal-single-shot-358395.html

double gun in auction http://aukro.cz/pruska-brokovnice-dreyse-plne-funkcni-pred-1890-i6415828579.html
caliber given as 20/20 so probably a 0,70", old style locking spring points to the early 1870s