I have a similar Hammer gun. But with 16ga 2 1/2 chambers with lengthened forcing cones. I have used the federal brand low velocity in the gun, but would opt for the Polywad low pressure. I believe your gun would not be too choosey about the ammo in proper chamber length. The german fodder was not very low pressure in the '30s and 40's. Fiochi, Westley Richards, and S&B are around. About the same price. If your gun is a late 30s or early 40s of good quality (I see it is very very nice), you have ammo choice. The 12 ga is a more popular chamber in the US. If the chamber job is done by a reputable name smith (Briley, Keith Kercher, etc.) I don't see this as much of a deterent to value.
I like the 9.3x72. Mine is one. I have shot the S&B loads. They are mild. They seem to shoot pretty well. I also have RWS loads. They are HOT. My gun was Proofed with 1939 German proof marks. I don't think the original gun was that new. I think I have newer barrels than the original.
I am working on some CAST loads and then some reloads of jacketed bullet. The cartridge standard is a 193 = 200 grain bullet. Your sights will likey regulate to that. I would suspect that the S&B shoot a little high. Let me know.
This is a great Boar, deer, similar size game gun. If you are a regular on this Blog, You will find several "Daryl" posts that will tell you how to work up BALL loads for those smooth bore barrels. Even with the full chokes. They will also be usable accuracy out to 50 or so yards. This makes the great "brush" gun or the fun Boar gun. I know that I will be venturing into the Thick with my drilling or cape with such a combo.