Hoot,
Here is how I solved the problem. Hope it isn't more than anyone wanted to know.
I started by slugging the bore and doing a chamber cast of my Emil Kerner rifle. This confirmed that I had the right cartridge.
I found a set of beat up 9.3x72R dies on eBay and shortened the FL die so that I could size cases sufficiently to chamber them. From some old 9.3x72R cases I made three test cases that I outside neck turned to get a proper neck thickness. Finally, I reduced the length of three .358 cast bullets so that they weighed 206 grains, paper patched them up to .366 and fired them. These three cases were sent to Hornady and a three die set was made.
The outside neck turning resulted in mediocre cases and when the dies arrived I could make good ones. The outside neck turned cases are used for shooting light round ball loads.
New RWS 9.3x72R cases were marked with a felt tip at about 60mm and using a disk sander I aggressively shortened the cases to this mark. The necks turned a dull red for a short distance from the cut end and slight heating could be felt at the head. The cases were allowed to air cool and then were trimmed to 57mm on a case turner. The heating resulting in sufficient annealing and length trimming was not difficult.
I determined that my inside neck diameter needed to be .362 and ordered an inside neck reamer from Forster. Because the long original case was shortened so much wall thickness was significant in the shorter version. The neck reamer leaves a shoulder inside the case but it is slightly below the seating depth of my bullet.
Steve Brooks made an ungrooved bullet mould for me that casts 209 grain bullets that patch up to .366.
Some final cartridges and the results.
I have some work to do with the vertical stringing and Petrov suggested that my forearm positioning on the rest was inconsistent.
Dennis