RCBS LOCK-OUT DIE 87540
The Lock-Out Die detects a "no powder" or a "double charge" condition in the progressive reloading process. It locks up, halting the travel of the ram at the case mouth, and alerting the reloader to the problem so the cause can be corrected. Will not let you continue without removing the improperly charged cartridge.
For use with straight-wall pistol calibers, and only on progressive presses.