RCBS Gold Medal Series of neck bushing rifle die is a 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 self-centering, 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". The Gold Medal rifle dies are available in Full-Length and Neck sizing styles. By removing the neck bushing, the Full-Length sizing die can be used as a "bump" die to set headspace back the desired amount. Neck bushings are not included. Proper neck bushing size can be determined two ways. Measure the outside neck diameter of your loaded cartridge, subtract .002" to .003". This allows approximately .001" of brass to spring back for correct neck tension. The other is to measure the neck wall thickness of your case, multiply by two, add the diameter of your bullet and subtract .001". RCBS suggests that you have neck bushings one to two sizes above and below your target diameter. The Gold Medal seat dies feature a micrometer adjustable, free floating and self centering bullet seating system with a convenient bullet loading window. The Gold Medal seat die can also be used on progressive presses with the exception of the .221 Rem Fireball, .17 Rem Fireball and .22 Hornet cartridge