Re: Case Trimming
I don't see any implications that trimming shouldn't be done, at least early in preps/forming.
But it would be a real pain(to re-trim & re-chamfer well), and sometimes unnecessary to do frequently.
It's an indicator of brass changing, as it's being trimmed away, and I for one prefer that my brass does not change at all.
I also do not like huge clearances from chamber end, as this contributes to excess sooting and higher ES. So I would not trim brass to some unknown, or inappropriate value for MY chamber.
If you have to do a lot of FL sizing, you're gonna have trim more frequently, so you might as well set up a good process for it. All we do IS a choice,, one leading to others.