This sporting weapon never passed thru any of the Austro-Hungarian proofhouses. And as far as I have seen, Emil Kerner did not have a Zella-Mehlis address so the probability of it passing thru the Z-M facility is quite small. I would expect to see a date-code on it if it did. Like I said this is a F.W. Keler sourced hammergun, or components and it maybe that there is a K on the tube above the crown over S or it could be a H. Compare it to the F.W. Keler Hahndoppelflinte. The stylized S you note is probably for a Schilling mechanic as the tail strikes back across the S but many times there is a brace. Is there a monogram on the left side of the aft lug or on the standing breech? The P mechanic probably supplied the forend hanger components.
Kind Regards,
Raimey
rse