The Expanding Mandrel Die from L.E. Wilson is designed for precision reloaders who want consistent neck tension and repeatable bullet seating. This die expands the case neck to a controlled diameter slightly under bullet size, creating uniform neck tension without overworking the brass. An expanding mandrel die is especially effective when preparing new brass, which is often distorted during bulk shipping, or when establishing consistent neck dimensions prior to first firing. By setting neck diameter before seating, this tool helps eliminate variations that can affect bullet alignment, seating depth, and overall accuracy. The die features a cut-out body design that provides clear visual alignment during setup, making depth adjustment straightforward and repeatable. Interchangeable mandrels (sold separately) allow the die to be configured for multiple calibers, while stainless steel construction ensures long-term durability and corrosion resistance. Compatible with standard 7/8-14 reloading presses, the Expanding Mandrel Die includes a precision-manufactured L.E. Wilson lock nut to maintain consistent settings once adjusted.