Hornady® Match GradeTM Bushing Dies allow the use of interchangeable neck bushings (sold separately). This allows versatility with neck size based on your preferences for neck tension. The bushing size will depend on your brass neck thickness and can be determined several different ways.
One way is to measure the outside diameter of the neck of a loaded round. Subtract .002 to .003 (or your preferred neck tension +.001) from the neck diameter to determine bushing size. This allows brass spring back and a neck tension of .001 to .002.
Example: Loaded neck diameter is .334 - .002 = .332 neck bushing.
Another way to determine brass neck thickness is to use the Hornady® Neck Wall Thickness Gauge (No. 041223) or a ball micrometer to measure the neck thickness of a case. Take that measurement, multiply by two, add bullet diameter and subtract .002 (or your preferred neck tension +.001). Example: Neck thickness is
.013 x 2 = .026 + .308 bullet = .334 - .002 = .332 neck bushing.
It is recommended to have neck bushings a size above and below the target bushing size. Brass may spring back more or less depending on unforeseen factors.