Like another post said, the .40 brass is from mainly unsupported chambers and has what I call an incipient bulge at the head of the case. The Glocks are the worst.
My son and I shoot and reload both 9mm and .40 and my hot nine mm Power Pistol load is his target 40 S & W power pistol load. So when he swaps out my powdermeasure to his .40 tool head everything works fine when I get it back.
Until he started getting what I call out of battery discharges that damage his gun. He too is shooting a not fully supported chamber gun. He now buys new .40 ammo and instead of ME getting the CZ 40 I wanted (fully supported chamber) I got a .45 which Ii can reload with scrounged brass,and HAVE been since '64 without worry
I wont reload .40. PERIOD
Yodar