The choice between bushing and non-bushing dies: Bushing dies allow for the adjustment of neck tension and they also allow you to get rid of the inaccurate expander ball. Non-bushing dies require a reamer cut to the exact dimensions for your specific neck tension. When choosing a non-bushing die choose the next die length. Example: a 308 Win. takes a 30 Cal. #3 sizing die, you should order a 30 Cal #4 for a non-bushing die.