You have what is known, by Americans, as a "clamshell" action double rifle in 9.3x74R caliber, no doubt one of the very best, if not the best caliber ever created by the Germans, especially in classic early calibers, and that is why it remains so popular even today in Europe. The most common bullet weight for this caliber was and still is 286 grains @ 2300 fps. That weight may shoot well in your rifle. "Clamshell" or stabil actions were made for various calibers, up to and including the .600 N.E., even though that caliber wasn't German. They are very strong actions, obviously---I have several myself, and have seen many others, yet have not seen a single one that was off face or otherwise not as tight as new. At first, when I first encountered these actions, I did not find them too attractive, but they grew on me over time, and I think they will too on other interested people, and they last forever, it seems. One finds an assortement of different names on these actions, names of early day German gun makers, and names of gun retailers as well, who did no gun making at all. Gun experts in Germany and elsewhere, now think that these clamshell actions were made by only one single foundry firm, probably at Sauer, (research was done on that, in Germany, but it could not be determined, for sure, who made these actions), and sold to numerous gun makers who completed the rifles, from outsourced parts they acquired, bought, and put their names on completed guns/rifles. Some dealers too, who did not make the rifles at all, did no work on them, but still had their names engraved on them, so the names on these rifles means only that such names are names of early day gunmakers or dealers, most of whom little or no information on them can be found today, due to poor records kept by these makers/dealers, or such records being destroyed during WWII, and/or due to results of our actions against Germany following and during WWII. The proof marks show your rifle to be made AFTER 1912, when the German proof house first started to use the stamp showing bullet type and weight (bullet type USED FOR PROOF; not used for service daily use, "ST MG" over bullet weight in grams; that bullet weight is regulation bullet weight too) ST MG means steel metal jacket, and bullet weight on yours says "18,9" --18.9 grams, if I am seeing it correctly. 18.9 grams = 291.6 grains. I can't read, see clearly, the other proof marks you are trying to show, but crown over N or word nitro was used for nitro guns. Yours is certainly a nitro rifle. From 1891 to 1939, bore (not groove) dia. in mm is shown, 8,8 meaning 8.8 mm for 9.3 mm caliber. Your rifle was, no doubt, made between WWI and WWII. It is highly likely that no more clamshell actions will ever be made, so take care of the one you have, and enjoy it.