If I want to find the problem I would cut the neck off . If I still had the problem I would shim the case and resize it I never have see a casewith the head expanded that didn't stick in the chamber to where I didn't have to bump it out only been loading since 1957I have been reading this thread and it really sounds like CH Luke needs a Vernier Ball Micrometer 1".
I would suggest he take several reading on New unfired brass at the Brass mouth and then down inside the neck
appx .200 . ( I believe this would be a base line to compare Fired brass to). Then, do the same on Fired Brass before tumbling in the SS media for cleaning. And then again on the fired brass after being tumbled in the SS media. I would suggest the reading be taken in several places on each piece of brass. And then again after Sizing the brass. If the brass wall thickness is appx the same thru all of these steps then something is happening in the Seating process.
CH Luke stated in a previous post that he pulled bullets and resized a Piece of brass a second time that exhibited the problem and then used a Standard Seating die vs the Competition die and then measured the diameter of the seated round and it still measures .343 at the neck mouth.
One thought comes to mind and that is that Competition and the Std Seating dies have standard seating stems in them and the .308 200gr hybrid berger bullet is a VLD style shaped bullet and possibly that is some how contributing to the issue??
I don't think I would be trimming necks until I knew what was causing this problem as he stated, this has happened on 2 chambers.
It is not a problem on new Brass, only fired brass that has been annealed, cleaned in a SS tumbler and then sized.
I welcome thoughts, comments on my thoughts as I have only been reloading for a couple of years myself.
My new dasher I had to shorten the die so I could close the bolt easy . I shined one case and resize it problem solved . Larry