From what I see it is a nice little drilling in 9.3x72Rx 16ga nitro proofed in Suhl.
The safety is a pretty standard Greener side safety and what looks to be a safety on the top tang is only a selector for the rifle barrel. With the selector forward the rear sight comes up and the forward trigger fires the rifle barrel and the rear trigger/left shotgun barrels is still available, sliding the barrel selector back makes the right shotgun barrel again available. Even the barrel selector on my hammer drilling(Zehla-Mahalis Guild gun) works the same only there is no side safety. My Post war Sauer is set up the same as your drilling.
What looks to be a safety on my hammer drilling is just a selector.
Standard S&B ammo should work just fine in your 9.3x72R. The S&B ammo has a stepped bullet to compensate the many types of rifling in the 9.3x72 bores. Mine has a bore diameter of .344 and a groove diameter of .364 which I think was originally built for lead bullets. Hawk(soft copper) and Buffalo Arms(stepped) have 200gr bullets appropriate for the 9.3x72R
Far right 9.3x72R S&B with stepped bullet.
2.5" 16ga shells are available from RST and Ballistic Products has components and data for handloading 2.5" 16ga. I took a 2.5" 16ga French sxs duck hunting with light #6 ITX loads and had a great time.
A JP Sauer should have what looks to be a Caveman holding a club for their logo usually on the exposed face of a locking lug. There are very many what are known as Guild Guns made by local gun makers that are not marked for manufacturer.
Link to help decipher German proof marks.
http://shotguns.se/html/germany.html