Hi Bob,
Got into Dixons European sporting cartridges pg 100 & the 11.5x51.5R Target is about the closest comparison I have come up with so far
------Casting------- 11.5x51.5R
Bullet dia.----- .442-------- .453
Neck dia.------ .462-------- .480
Case length--- 2.040-------- 2.028
Rim dia.------- .590-------- .598
Base dia.------ .503-------- .503

GSP53: Lorenz case #182 shown only in the 1886 Export catalog as a target cartridge, dimensions taken from the catalog and are only approximations.

Hope this may be of some help
m4220
Mike