I read about this over on the M1896 Mauser Forum; at least one member has such a Mauser Broomhandle chambered in it...I Googled it, and found a couple other references to it (it's supposed to be a very rare chambering, like the 7.65 Luger cartridge in the C96)...
http://1896mauser.com/forum/viewtopic.php?t=885
http://1896mauser.com/forum/viewtopic.php?t=888
But I can't find any pics...Does anyone have a pic of it??? Is it a bottleneck like the 7.63 Mauser cartridge??? It works out to ~.320"...Pretty much in between 7.63mm and 9mm...
Sounds interesting...