Just flair enough to get bullet seated
The flair should be just enough to where you don't shave any lead or coating.
I say: Flare enough to be SURE you don't scrape up coating, jacket, or lead.
Of course the case mouth with bullet balanced has to go in the seating die, but that is all.
I don't worry about "brass life" I figure I will lose it before I wear it out. When I do manage to recycle a case enough to wear it out, a 9mm or .45 ACP will usually crack in the sidewall, not at the mouth, so flare and crimp are not really a factor.
Your choice of components will affect your choice and adjustment of dies.
Me?
For 9mm I have a regular carbide sizing die, the regular Dillon "powder funnel" expander, a Hornady Microjust seating die, and a Lee Carbide Factory Crimp die. This gives me reliable ammo with mixed brass and 124 gr coated lead bullets. You can see the burnished bands on the loaded rounds where the CFC post-sizes. Most come out with a rub band near the rim where the CFC die has less mouth radius than the Dillon sizing die. Thick brass or a larger bullet will show a band over the bullet. Probably swaging the bullet a bit, but I demand free chambering. If it hurts accuracy, too bad, my targets are generous. If I were shooting bullseye, I would use better bullets and brass.
When I load an occasional batch of 115 gr JHPs for defense gun practice, I substitute a Lee/EGW "U" undersize sizing die to get a good grip on the short slick bullets. The Hornady die is much more convenient to adjust seating depth with than the Dillon die and less expensive than the deluxe Redding.
I tried one of those aftermarket powder funnels said to give a step expansion like a Lyman M die but the step is almost imperceptible and it just didn't work.
For .45 ACP I use a regular carbide sizing die, the regular powder funnel, a Hornady seating die, and a regular taper crimp die. This gives good ammo with mixed brass and 200 gr coated lead bullets. I gauge 100% and anything that fails the gauge goes through a Lee CFC die in the single stage press. For loading 185-200 gr jacketed bullets, I pre-size cases in a "U" die. I don't leave the U die and CFC die on the progressive, it increases the effort on the handle more than I want to wrestle with. Fortunately I don't have many gauge rejects and I don't load many jacketed bullets, because I hate double handling ammo off the progressive loader.
