This dummy is a danish reload.
After WWII, the Danes did use German K98 rifles ,and also BESA mgs in tanks they had obtain to reorganze their armed forces, for a couple of years. A good quantity of ex-German cases were at hand, and they reloaded them as natural wood bulleted blanks (also ex-British ones).
Same case were also reworked as dummies, with three ID rings engraved around lower part of the case.
Both reloads were done by A/S/ Dansk Ammunitionsfabrik, in Otterup, this facility using a circular mark overprinted on the headstamp, as seen on your picture.
I do not know the exact designation of this dummy, but the blank variation was called 7,92 mm lospatron m.1947, which indicates that this ammo was still in use more than two years after the end of WW II. Maybe one of our Scandinavian member could add something, or correct my post?
(sorry, in the word “lospatron”, the o has an oblique slash, for “oe” spelling, but I do not have this danish letter available here)