We should get together and do a group buy to get Joe's style expanders made up and then all you need are gage pins and collett's.
Is anyone using the Sinclair expanders? A 20$ die body with a removable cap that actually gives the 12$ Sinclair expander mandrel (already beveled) a little bit of wiggle room to self center.
These mandrels are available in every caliber. Simply chuck it up in a drill and wet sand with a little 400 grit then 600 grit sandpaper when they arrive and you will have uniform and concentric neck tension.