The rifle seems, due to its overall appearance, to be an original pre-WWII rifle, only the diopter was installed at a later date. As far as I know, original rifles of this caliber were only produced until before the WWII. There are few modern rifles caliber 11,2x72 Schüler made, above all by Harald Wolf in Belgium, but there must be very few of them. Does not make much sense either, the cartridge is a little outdated compared to what cartridges are available today for big bore rifles. Rifles of this caliber are primarily matters for aficionados and collectors.
It's difficult to say, only based on the photos, who built this rifle; the gunmaker Tenhaeff in Utrecht or a gunmaker in Germany, maybe in Suhl, for Tenhaeff.