Re: Get a GRIP! (on the bullet.... that is).
The Lee Collet die is an exelent neck die. You are correct it does not have an expander button , the case mouth is squeezed around the mandrel. The Lee die is set up from the factory for about .001 neck tension. Many feel this is not enough "grip". One can increase the "grip" by chucking the mandrel in a drill and polishing it down a thou or two. Or you can call Lee and order a reduced mandrel for $5.
It may be that you are feeling the difference when seating because of to little neck tension instead of to much.