[Bart B.]

Few folks really understand how a bottleneck case that headspaces on its shoulder fits the chamber when it's fired. Doesn't matter how much clearance there is between the chamber neck and case neck. They all center perfectly in the chamber neck floating in space with some clearance around the case neck to the chamber neck. Even in a .308 Win. chamber, .243 Win, .260 Rem and 7mm-08 rounds chambered in it will all have their necks well aligned in the chamber center should they be fired in it. Same thing for .25-06 and .270 Win rounds in a .30-06 chamber. These round's necks float in the middle of the chamber when the bolt's closed on many rifles and all of them when the round's fired. Rimless bottleneck rounds do not rest in the bottom of the chamber when the bolt's closed on them. Nor are they in that place when they're fired. Check out your rifles and see were all the forces come from that position a round in the chamber. It's easy to do if you just look at the hardware and know how it works.

Nor does it matter how uniform the case neck wall thickness is; less than .0015" spread's enough for excellent accuacy. It's more important that case necks be well centered on case shoulders. Full length sizing fired cases does a better job of doing this than neck only sizing.