Charles
That I would, Licensed Clinical Psychologist and do Forensic work as well.
Since the 9.3 x 57 and the 9 x 57 Mauser are necked up versions of the 7.9 (8mm) x 57 Mauser the body taper and neck appears identical in the pictures.
COTW lists the following loads
232 SP IMR 3031 47gr 2330mv 2785me
286 SP IMR 3031 43gr 2070mv 2705me
286 SP FL 2065 2714 (factory load)
I'd take the lightest bullet you have loads for, drop the load by 15%, neck up the case and give it a try. You will find out the shape of your chamber at least.
Either that or do a chamber cast with the stuff from Brownells. Then compare the chamber cast to your necked up cases and see how they compare.
Wayne the Shrink