Thread: Case neck sizing and effect on accuracy

How much of the case neck do you size?

On one hand, if full-length sizing using the die from a regular 2-piece set hard down onto the shell holder, a round using a case sized with this arrangement when chambered is presumably held in position at just the the two ends - by the case head on the bolt face, and the bullet shank in the freebore.

When the die is backed off the shell holder, or a bushing die is used, then there is the choice of how far down the neck to size. The unsized portion of the neck will remain at the fired diameter and help centre the top of the case, or at least that is the theory as I understand it. Depending on how much the case walls and shoulders have been taken back in, this may remain the only part of the case above the head that is a close fit to the chamber.

Then there is the question as to how much of the neck provides the ideal support for the bullet. Do long necks aid accuracy as is often proposed? If so then why have the bullet only supported by a fraction of the available neck? Maybe the advantage of long necks is to allow for both a section of neck left unsized for the above mentioned “centering” but with 4-5mm still left for the bullet? Maybe long necks aid accuracy only by a beneficial effect on throat erosion?

What is your thinking on this and why ?