Your rifle was certainly put together post-WW1 in the Suhl/Zella-Mehlis area. The stock style is typical for the guntrade of that area. If the small-ring receiver is indeed inscribed "Waffenfabrik Mauser Oberndorf a.N."it may indeed be a commercial transitional receiver. The Triggerguard and set triggers at least look "Commercial Mauser" to me. How to identify Mauser commercial parts, see my post on the "Carl Grundig" thread in the "Mauser Forum".Have a look at the proofmarks too, perhaps there is a date stamp?
The bolt sleeve at least is not "Transitional" as the bolt-sleeve lock housing is visible in one of your photos. imho the rifle was most likely put together in the 1920s using a Karabiner 98a action together with a left-over commercial Mauser magazine box/set trigger assembly. But it may have been reworked or rebarreled even later, post-WW2.