Some examples of what the receiver undersides of commercial Mauser, Oberndorf actions sold to other gunmakers look like:
Mauser #17 on an early cock on closing transitional action, rifle by Sauer & Sohn, Suhl. The lowest Mauser number I have seen. #19 is on a Rigby rifle.

#114 Rigby #1059

#199 Rigby #2457

#279 on a Sauer & Sohn rifle

#19759 on a Suhl made rifle retailed by Hermann Franck in Magdeburg

#22064 by W. Foerster, Berlin

#49784 retailed by W. Bening in Wilhelmshafen, but Suhl made also

#74352