450 Bushmaster Die Set brand new in 2019 from RCBS. This changeable diameter neck bushing type of die has been used by Bench Rest and Long Range Precision shooters for years. Due to variability in neck brass thickness, RCBS standard dies size the neck below your desired diameter and then pull an expander ball through to get the proper bullet tension. The Gold Medal sizing die features a selfcentering, changeable neck bushing that allows you to precisely set the amount of tension on the bullet. This reduces work hardening of the case neck brass, prolonging case life and increasing accuracy. Neck bushings are available in .001? increments from .189? to .365?.