Originally Posted by BrentM
To clarify, are you saying to size the neck significantly under diameter and run a ball back up the neck to expand it to proper tension is the best way?
I guess it depends on whether you agree with the experts who write the books or the experts who write on forums. The books all indicate that neck sizing is a proven method to increase accuracy and case life. Proper neck sizing involves bushings to resize the neck to .002 to .003 under the loaded case neck diameter.
I agree with the folks winning matches and setting records and getting best results testing bullets for accuracy
With bottleneck cases headspacing on their shoulder, the case neck and the bullet in it are centered in the chamber based on how well centered the case neck is on the case shoulder. With such ammo, the case shoulder's hard into and well centered in the chamber shoulder when the round fires. In line ejectors push it there before the firing pin drives it there when it fires. The case body doesn't touch the chamber at all except at its back end where it's pressed against the chamber wall opposite the extractor on the case head. The case neck floats in space in the chamber neck. How well the bullet aligns with the bore is decided by how perfectly centered the case neck is on the case shoulder.
Full length sizing dies with neck diameters a couple thousandths less than a loaded round's neck diameter best center sized case neck on shoulders. They hold the neck sizing part of the die well aligned with the body of case centered in the die body. Neck only sizing dies don't do that. Tension's determined by how much smaller the sized case mouth is than bullet diameter.
Few top ranked, match winning and record setting rifle shooters write books. Nancy Tompkin's one of them. She, her husband Middleton and daughters Michelle and Sherri have probably won more matches and set more records that any other group of four people on this planet. They've been doing it with full length sized bottleneck cases for decades.
Sierra Bullets' been full length sizing all their cases used to test their stuff for accuracy since the 1950's. I doubt anyone shoots their stuff more accurate than they do. Most benchresters switched over to full length sizing their cases a few years ago. While their smallest groups stayed the same size, their largest ones shrank quite a bit.
I've observed over the years that brand new cases, both rimless and belted ones unprepped in any way, typically shoot bullets more accurate than any neck only sizing ones do. But I judge accuracy by where all shots fall, not just a small cluster of a few of them dead center in a larger group of shot holes. Any fired case sizing process will sometimes put a few shots in the smallest group their maker has ever seen.