The necks will harden with use,there comes a time in the life of case when you either anneal or F/L.

I just used some scotchbrite which is a fancy name for steel wool. It don't take much, you need to measure often. For 5 bucks Lee sells undersize mandrels. You need a press that can exert some heavy pressure too. I toun mine 1/3 of a turn and do them 3 times.

Ditto Val's. I called Lee and they made me up a 0.2615" to replace the 0.2625" mandrell that came with the die. I like it a lot better, and it cost me $9 - $5 for the piece and $4 for shipping.

It wasn't just the fit of the bullet that improved, though that did too, but the feel of the sizing action itself became more positive. I can feel something happening now, and I could not previously.

Jaywalker