Cottage industry Mausers were very common in German History from after both WW1 and later after WW2 also.
Every county had their own proof house which had to comply with National proofs, but then the maker had their proof station too. So proof marks on Sporting Mausers are prolific, and there are ways to track them all down, but I don't have the resources to do it myself.

Keep in mind, the old bore size from pre-1905 was .318" After 1905 all military Mausers went to .323" BUT not all Sporting Mausers did until the late 1960s. .318 was as common as 323" for hunters in German for over 60 years!
Your barrel was made originally as a sporting barrel, but CHECK to see what the groove diameter is. THAT'S VITAL.

If you have one with the old 318" bore it's not a problem that you can't overcome. PPU and DWM as well as Seller and Bellot all make ammo for the old 318" size to this day, and if you hand-load you can buy them from several manufacturers in other places. No US Company makes .318 diameter bullets, but there are several importers.

You rifle is a REAL hunters rifle. If it were mine I would be out killing deer, elk and antelope with it for sure.