lee expanders are made for the shorter/thinner jacketed bullets. A factory lee expander next to a custom expander.


A factory lyman m-die/9mm's


The 2 main reasons for reloaded 9mm ammo to fail:
Bullet started/seated crooked from the expander being too small/not expanding deep enough.
Case springback, different lots of brass have different hardness. Add to that work hardening of the brass from multiple reloads. Springback in the web area of the case is more common.

You might want to run a magnet over that s&b brass.