African Outfitter Magazine

http://www.africanoutfitter.com/

Dec/Jan 2009 issue has a rather comprehensive article on the .500 Jeffrey/Schuler. Well worth getting a copy.

It states that there are a number of different chamberings and designs of ammunition. Some early ammo had a rebated rim and later ammo did not. The rebated rim seems to have had some feeding problems. With modern rifles with modern ammo one would hope that any differences have been eliminated.