Sorry I'm not much good at guessing. Franz Jaeger moved from New York City sometime after 1901 returning to Suhl, he has a USA patent as Franz Jäger (German spelling) from 1906 with a Suhl address.
I know of a S.R. Griffin with this mount on it so that would would put it before 1923 if the mount was installed the same time the rifle was made.
I did not do a lot of research on "Franz Jäger" but spent my time on the son Paul. Maybe one of the students of German guns has other Jager catalogs and can date this mount.
It's interesting to me that the cut from the catalog shows this mount on a custom 1903 Springfield.
