I am trying to learn something new or better every day. make a quick internet research and found this:http://proofhouse.com/cm/codes_markings.htm "KABA, KABA SPEZIAL Tradenames of Karl Bauer, a Berlin, Germany dealer. Handguns made by Menz, August and Arizmendi, Francisco bear this name."

must say that I remember karl barthel for kaba from a read some years ago about 16 ga shotguns make from WW 1 surplus mauser rifles from the backyard of my brain. and now when you say this , yes,it was barthelmes. what we know is that there is special typ of hunting rifle with a shotgun style triggerguard. the stock for this rifle's was coming from the same hand's. I have showing such example's in 9,3x57 and 10,75x57 here.follow the swedish website one rifle was marked also kaba beside of the geco stamp. also to note that kaba and geco had have rimfire rifle's with such a shotgun style triggerguard.
I am being with you about the very complicated situation in suhl/ zella-mellis.

this description here was going so close to my own words that I believe now this guy was making also a short internet research to look what he was having and read my post on nitro express before the rifle was going to egun:
http://www.egun.de/market/item.php?id=2647291
"Sehr seltene Mauser 98 im Kal. 10,75x57 der Fa. Karl Barthel. Die Firma Karl Barthel hat für Geco bis zum zweiten Weltkrieg in Suhl diese Waffen hergestellt. Viele dieser Gewehre waren für den Export gebaut worden. Das Gewehr ist in einen guten Gebrauchszustand. Alle Metallteile sind in einem guten bis sehr guten Zustand, Der Schaft weißt stärkere Gebrauchsspuren auf.

Aufgrund der vielen Nachfragen nochmal, es handelt sich wirklich um das Kaliber 10,75x57 !!!!!!!!!!!!!!!!!!!!"

I have seen till now pics from 3 rifle's in 10,75 x57, including my own and all were of the same model.