Here is a handy little spreadsheet for calculating the thickness of neck brass after you have resized it for a different diameter bullet.
Several times, I have resized 308 to 243, and have never had any problems with the brass not chambering correctly. But if you're curious, this will put numbers on the amount of change.
For example, if you go from 308 to 7mm-08, you pick up a bit more than .001" in neck brass thickness.
'Four legs good, two legs baaaad." ---------------------------------------------- "Jimmy, some of it's magic, Some of it's tragic, But I had a good life all the way." (Jimmy Buffett)
I neck down 30/06 brass to 257 Roberts. Since the 30/06 shoulder is now the neck, I have use an inside neck reamer. The reamer came with the conversion kit.
If you reload, there's no such thing as an obsolete cartridge.
Once you render an opinion, you open yourself up to criticism.