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Folks winning matches and setting records in NRA high power rifle matches have been doing so with proper full length sizing dies for decades. The die's neck is about .002" smaller than a loaded rounds neck diameter; RCBS or Redding full bushing dies are the best commercial ones made these days that do that. And the fired case shoulder is set back no more than .002" New belted cases have produced as good of accuracy as proper full length sized ones that have the. Accuracy attained testing rifles and ammo has equalled what long range benchresters get these days.
Benchresters neck only sized for decades, but they've recently switched over to full length sizing for the most part. The dies they use reduce case diameters and set shoulders back only .001", but that's enough. Their smallest groups are still as tiny as ever. But their largest groups are now a whole lot smaller.
Sierra Bullets' been full length sizing all their bottleneck cases used to test their stuff for accuracy since the 1950's. I doubt anyone shoots their bullets as accurate as they do. Their best match bullets go into 1/4 MOA at their 200 yard test range. No case prep nor load work up is ever done; they use the same recipie for each new lot of components and test barrel.
What most folks don't realize is a full length sized bottleneck case headspacing on its shoulder centers up front in the chamber just as perfect as neck only sized ones when the round fires. And without the interference between case body and chamber walls and shoulder that so often happens. And fired case necks are more perfectly centered on full length sized bottleneck cases as the case body is held in perfect alignment with the case neck as the neck's sized down.
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