I've never bought a 9mm factory cartridge and never bought 9mm brass. I've only loaded range pick ups and have never had to trim brass. You should spend your energy doing a plunk test on your completed rounds using the barrel of your gun or a case gauge if you shoot multiple 9mm's. There are occasions where the brass is expanded more than usual at the base and you want to either cull those out after resizing or use a push through resizer because a fat case head can cause a stoppage while you're shooting. Nothing that a squib rod can't pound out but it's still better to catch those rounds before they go into your gun.