Ash ,
Wilhelm Brenneke was a pretty talented bloke, had a few patents for various mods to rifles & of course the family x64mm.

http://www.deutsches-jagd-lexikon.de/index.php?title=Brenneke,_Wilhelm

Jack Lott wrote a fair sized article on him & also small blurb on the 9.3x64mm in a magazine "big bore rifles" - I have that in .pdf form, but she's pretty tattered!
Were good articles - Jack Lott was a rather good writer!
Let me know if you want them, will take time to dig up
Cheers
93x64mm