I have never found the need to soften the necks and if you choose to try doing one case first to see if the mouth of the collapses. I have found the cases to last as long as the primer pockets do, some go quickly others seem to last forever.

JLouis

When breech-seating the cases should last "forever".   No reason to anneal -- and in fact, since it is so hard to do reproducibly, it is almost never a good idea.

The reason that case necks sometimes collapse is that with the bullet seated ahead of the case and the powder constrained by a wad, one sometimes gets a pressure pulse hitting the base of the bullet.    This is the same effect that can cause a little ring in the chamber, if the metal is thin or soft, from the accelerating gas hitting the base of the bullet.    The pressure wave reflects off the bullet base and back into the case.   The case neck has already relaxed, so some of the gas gets on the outside of it and caves the neck in.    This can be prevented by slightly flaring the neck of the case each time it is reloaded.

CHRIS
RGChristensen