I've completed a load workup for my 308 10FP, and found a good load. I used new FL sized, and prepped brass. I cleaned, deprimed and prepared to prep brass for reloading. Using the Lee neck sizing die, I adjusted down to the point where the neck will grab a 175SMK, and the casing will fall in and out of a Lyman headspace gauge. I had a stuck 223 case in my 12FCV last fall, so I thought I'd see if the empty 308 case would chamber. It wouldn't. I checked most of the empty 308s and they wouldn't chamber. I searched this forum and others concerning this issue. The fixes for fire formed cases that would not chamber ranged from using the neck sizing die properly, to FL sizing a second time. A couple of posters stated that the 2nd FL sizing resulted in a fired case that would chamber in their rifles. I know that an off the shelf rifle may not have a concentric chamber. If this has anything to do with this, how does a 2nd FL sizing fix it? I'm OK with FL sizing if I have to in order to avoid chambering problems at the range. I've also read that shot to shot consistency is better with FL sized brass. Neck sizers don't consistently size the shoulder? I guess this has turned into two questions. I'm interested in understanding why a fire formed case doesn't chamber in the same rifle. I've read the posts on proper use of a Lee collet die. I've followed the mfgr instructions and watched the Youtube videos and seem to be following proper procedure. Is there more to neck sizing than it appears? Should I FL size in order to stay out of trouble?