Does the taper looks like the one in the picture?
That is the barrel still attached to my BRNO Mauser Action. Military Spec barrel. Often called the Krupp Barrel, after the Krupp Munitions Firm of pre-WWII Germany.
If the barrel does not step/taper down again to near .500 diameter, then it has been cut down in length. Originial sights were soldered on.
I've heard of smiths filling in the stampings on the receiver to clean them up for resale as custom builds. If there are no stampings or markings on the action or barrel, then it is near impossible to trace date of origin.
Being 8mm, you can be sure it is pre-1945 for sure. Don't have any books on Mausers, so cannot give you any idea of run end dates for that caliber.