Normally you do not need to neck turn factory cases. factory chambers normally have anywhere from .004-.008 or more slop in them.
If anyone turns cases for factory and find that their sizing die does not work, they have two choices.
buy a Redding bushing die OR send their original die to Jim Carstenson at firstname.lastname@example.org
13095 450th ave
Bellevue, Iowa 52031
for $35 Jim will convert a standard die to redding bushings. He will also build a custom honed die from the $24 redding body bump die with neck bushings (cost is about $75). You can see his work on www.6mmbr.com
Great dies, I have about 4 sets.