This is a circa 1920 Mauser Model Gew. 98 8mm Bavarian Police rifle. This rifle was originally manufactured by Mauser A-G in Oberndorf A/N in 1905. It was subsequently officially reworked after WWI into a more modern rifle with new flat rear sights and other updated bits and pieces. It was marked "1920" on the receiver to indicate it was German Government property that complied with the postwar 1920 German Disarmament laws. This rifle was then issued to the Bavarian Citizen's Militia (Einwohnerwehr) that was controlled by the Bavarian Police and the Interior Minister.
Notice the "1920" Government property markings on the receiver which have nothing to do with the date the firearm was reworked. Also, notice the "EWB" branded marking on the stock indicating issue to the Bavarian Citizen's Militia (Einwohnerwehr). These reworked WWI rifles continued in use throughout WWII.