From following the 10.75 thread, I assumed it was related to the 8x68.

However, the wiki page turned me on to the 375 Holderlin. I can't find any other references (in English). Has anyone seen or worked with this chambering?

x68 Family

quote:

375 Holderlin

The .375 Hölderlin
The 8x68mm S case has functioned as the parent case for the .375 Hölderlin (9.5x68mm), which is essentially a 9.53 mm (.375 caliber) necked-up version of the 8x68mm S. The wildcat status of the .375 Hölderlin ended in 2007 when it got C.I.P. certified and became an officially registered and sanctioned member of the German 68 mm "family" of magnum rifle cartridges. If the .375 Hölderlin will become available as factory ammunition, like the older cartridge "family" members (8x68mm S and 6.5x68mm), is still unknown.

next to the 9,3x64B;

@trax

You're killing me, details pls. Your sig doesn't have a location, are you in Germany?

Was this a one-off or do you know of a functioning gun?

I like it! Very little info that I could find online, but all in all a great looking contender for a light sporter weight medium bore thumper.