Bucksticks,
I am going to second what Huvius said regarding web thickness. It seems as if you are well versed in this type of thing so I am sure that you thought about the amount of metal that you have left.

I was loading for the 8x58r Sauer ( I presume related to your 9mm) and found that the best cases to use were 303 brit commercial. It seems that the commercial brass is undersized in the web compared to military and it left me with a bit more metal to work with.
Still ended up having case head separation after about 3 rounds in the cape gun that they were loaded for.

Tom