My cases headspacing on shoulders are driven by firing pins full forward in the chamber against the chamber shoulder. There's clearance all around their body to the chamber except where their pressure ring is pressed against the chamber by the extractor.A cartridge can just lay in the bottom of the chamber, and this depends on case base diameter, chamber diameter and the type action. And the proof of this is the fired case will expand more on one side.
The thin part of the case body expands the most. It can be anywhere around the case as proved by firing pin imprint orientation showing how the case was in the chamber when fired.
None of my bolts do anything to hold the case head against their face. Theres a few to several thousandths clearance. This is done to ensure case shoulders can stop against chamber shoulders supporting the case for firing pin impact.
Please stop spreading myths.
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