These Redding Straight Wall Expander Dies contain a neck expander plug for use before the bullet seating process. Expander Dies flare the case mouth slightly to ease the bullet seating process. Dies are made using the finest alloy steels obtainable and machined on Hardinge Super-Precision lathes capable of holding the tightest tolerances in the industry. Heat treated in atmospherically controlled furnaces and hand polished for smooth, flawless functioning, these dies will maintain tolerances and last a lifetime.