Here in the western part of Germany 8x57IS Mausers without proofmarks are quite often seen. They are of two different periods, both post-war. After WW1 many military rifles ended up in now civilian hands. The conditions of the Versailles treaty demanded these guns to be surrendered to the government and destroyed, but sporting guns were not affected. So many of those M98 rifles and carbines were sporterised instead of surrendered. Usually all military markings were scrubbed off, sights were changed and either new stocks fitted or the original stocks altered. Nobody cared then to have these used military rifles civilian reproofed. Alas, Germany was in revolutionary turmoil and some proofhouses closed. A similar situation existed post-WW2. The landscape was littered with thrown away K98ks. Many of these were retrieved from the bushes, sporterised and restocked by unemployed gunsmithes and peddled for food or other conveniences to mostly GIs. Such rifles are known as "Cigarette Mausers" after the favorite barter in America. About 1950, when gun control relaxed and West Germans were allowed again to own and use hunting rifles, such cigarette Mausers were often the first hunting equipment. Older guns resurrected from the most unlikely hidings. Some of the old guns had to be restocked because rot. But proof laws and proofhouses were not yet firmly established. So noone cared about proof.
From the description as a scrubbed small ring Mauser action I suspect this rifle to be a sporterised WW1 98AZ carbine, maybe restocked again after WW2.