Re: Even neck tension
This is what expander balls are all about; uniform neck tension. It is also exactly what you'll accomplish by using an expander mandrel. In use, you simply run the case mouth up onto the mandrel, and it sizes it from the inside. This negaes any variation in neck wall thickness, which cause uneven tension if you've sized them only form the outside, i.e., using a bushing die without an expander ball.
I like bushing dies, since it allows me to control neck tension to precisely what I want. Many will advise that these also allow you to size without using an expander ball, which is true . . . sort of. Expander balls can cause all sorts of problems, but most of these relate to the use of dies which size the necks down far to tightly, and then brutally drag the expander back through the undersized nect, with bad results. Choose a bushing that sizes the necks down to the point where the expander just kissses the necks during their passage back out, and you'll get uniform neck tension while avoiding the problems normally associated with them (the expander balls).