here it is

no time just now but the case is similar to the 10,75x57, having a shoulder but case mouth helps a lot.

great find and better than the 11,2x60 Schüler you were looking for. the first rifle I ever seen for this cartridge.
wish it would be mine

Eduard Kettner start as a mail order house in Köln but had a work shop in Suhl than because it was a must have to be seen serious.
I have no doubt this rifle was made there. of course there a re a lot of similaritys with other rifles from Suhl in this time frame because such man like stockmaker, engravers working for everyone there.