The Wilson Expanding Mandrel Sizing Die. These dies are designed to be used on NEW brass cases to prepare the case for the seating operation. Over the past few years we have seen a greater need to run new brass cases over an expanding mandrel to properly prepare them for their first firing. New brass cases are often damaged when shipped in bulk, this die will give you a consistent neck diameter on your cases. With correct neck tension you can expect a more consistent seating depth. Includes one mandrel. Additional mandrels sold separately. Cut out in die provides an easy view for making sure case aligns and setting up depth Int Mfg: L.E. Wilson