Briman

I only use them on bottle neck cartridges. It sort of steps out the front edge of the case mouth a few thou, keeps it from shaving lead off the bullet, I use them for flat based jacketed bullets too. I haven't used them for pistol cartridges as the standard case mouth belling die does an adequate job by itself. A good way to use them if you are FL resizing, is to use a universal decapping die, then remove the expander ball from the resizing die and use an M die to reexpand the neck- you eliminate the possibility of uneven neck stretching that you can get from pulling an expander ball out of the neck.