Don't get caught up in the semantics of dukedom, kingdom and the like. Many of Valentin Christoph Schillings as well as Erdmann and Reinhold Schlegelmilch's(porcelain) examples have "Suhl Prussia".
Info on Suhl - "In 1718 the territory was owned by “Kursachsen”. Mining and the trade with arms declined initially. In exchange the “Barchenweberei” (weaving) and the adornment of weapons developed. Precious pieces of this artistry from Suhl master craftsmen, for example Stockmar can nowadays be seen in the museum “Grünes Gewölbe” in Dresden. Therefore the production of arms in Suhl also caused the town to prosper. 1751 is the year when “Sauer & Sohn” was founded. This was the first German factory of arms and after the Belgium “Lüttich” the second in Europe. Between 1756 and 1760 Suhl’s gunsmiths sold 25,000 rifles to Prussia. Because of this standing the town as well as the whole county of Henneberg joined the kingdom of Prussia." -
http://suhltrifft.de/content/view/16/639/lang,en/ I think Prussia existed from 1701 to 1918 and I've seen reference of Suhl being in "Prussian Saxony".
Are you reading the initials left to right or right to left? Are there any period beside the initials to tell which way they were stamped? Usually facing the tubes with the flats to the right the initials are read left to right. Also there looks to be another set of letter up toward the Lindner type forend lug on the right tube.
A sort of side note on air guns of Bergmann of Eisenwerke Gaggenau possibly made by C.G. Haenel or V.C. Schilling is that airrifles and possibly other longarm had a mark of "EG" over "Crossed Pistols".
Kind Regards,
Raimey
rse