Great info, thanks to all who contributed to this thread.
Correct me if I'm wrong here.
The way I understand this is the sized 9mm case is smaller than the .358" cast bullet so when setting the bullet in the case the brass will swage down the .358" bullet to a smaller size. This was noted to be .355" from the OP. By using the 38 S&W part, the brass will be wider (.356"?) so the cast bullet (.358") will not get swaged down by the brass case such that if you pull the bullet it will still be .358".
The amount of expansion is set to approx. .30" down from the top of the case.
Is that correct?
A thought occurred to me about using a fired non-resized 9mm cartridge instead. Perhaps it is enlarged enough from the firing expansion to accept the .358 cast bullet without doing the mod to the 9mm die. This would keep the tapered case dimension rather than changing it with a straight .30" expansion area if doing it with the modded die.
Thoughts?
Thanks.