More pictures of a .280 Halger:
https://www.feine-jagdwaffen.de/Waffengalerie/Archiv/Repetierer

A 7x64 Brenneke in a Magnum Action makes no sense.
The 7x64 needed only a slightly longer Magazine box ( 88mm) in a standard action length.

I used the wrong word typo , what I wanted to say is:The different kind of lettering 7X and the small 64 .
Canīt believe that it was the original designation.
They certainly had the correct lettering stamps , when they marked the barell first.
The barell is modified from the Original configuration in more than bore and chamber.
The rear part of the(milled down)rib is so poorly matted , that I canīt imagine as the work of so qualified smiths like Hoffmann/Howe or Mahillon .
Could you measure the Magazine box internally (length,rear and front width) to narrow down its original intention to be used for.