Re: 338 lapua neck loose
Do you turn your necks? You may be turning off too much material for that die, and you will need a bushing set-up.
If this is the same die you have been using successfully, I would first suspect a work hardening of the brass. What do you use to anneal?
I wouldn't modify my die until I figured out what was going on, then change what needs changed. Have you taken a micrometer and measured the expander ball? How about your bullets?
Just some thoughts.