That die setting that moves the shoulders of perfectly good brass 10 thou will fail to move the shoulder of an overstretched piece sufficiently. This is exactly what is being described.
Because springback. Folks tend to think dies move all pieces the same at a particular setting. Not so.
Which leaves you wondering if you need a SB die. So you can move shoulders......probably less. But works the brass more. Which shortens brass life on the good pieces that didn't need a SB die. The overstretched pieces then fit in your gun......great!!........whoops partial separation on first fire???
Cull the overstretched pieces first. Then you won't need a SB die. Then you can use your die to bump shoulders just enough. Then you won't have short brass life.
Last edited by Sam_H; 06/13/21.
