Superior to “ball expanders,” this Hornady exclusive provides extremely smooth neck sizing and significantly reduces friction and case neck stretch. Internal threading prevents it from pulling loose and the elliptical expander also eliminates the need for a separate expander die for necking-up to the next calibre.
Elliptical expanders which are only used in bottleneck cartridges will be the retainer for the decapping pin in your Hornady dies. In most cases, the expander is going to be .001” under the bullet calibre diameter. (For example, a .224” diameter bullet would use a .223” expander.)