when I get new pistol cases I size and then trim to the same case length as my others so I don't have to adjust my dies ,but I always trim before I flare
usually they will crack before they stretch that much and then you'll need to aneal them, the .357/44 mag cases that is. True enough the taper crimps in pistol I've never done.
If you are using a roll crimp and want consistent loads you will need to trim all cases to one length (if cases very in length at all) so you get a consistent crimp every time.
Anyone ever have any problems with Lee dies crimping .357 mag? Every once in a while i will get one that crimps but im able to spin the bullet with my fingers. I wondered if the brass was a little long.