This is the Dillon Precision Bullet Feeder Bullet Drop Die.  This allows you to keep the die set up in your Dillon XL 750, XL 650, RL 1100, and Super 1050 toolhead and move the bullet feeder to load another cartridge.

Function: Acts as a bullet drop die in the automated bullet feeder setup, allowing you to keep the die threaded and set up in your toolhead while switching calibers or adjusting your process.

Dillon Part #: 91103