Just a question on this. Would your brass eventually stretch to your chamber dimensions with FL resizing if your just bumping the shoulder back from the fired measurement?
Lonewolf, there is actually no reason to bump the shoulder at all until you get a crush fit, you are just lengthening the process of shoulder growth to fit your chamber, especially on belted cases. Belted cases have much more...shall we call it shoulder advancement ... than an unbelted one. The reason is that belted cases
headspace on the belt and not the shoulder. The brass manufacturers have no reason to manufacture the case so that the shoulder position is close to chamber dimensions because the belt stops the forward movement of the case
For example a typical series of firings on a belted magnum results in the following measurements
300 win mag Mato
new case measurement - CBTO 2.253"
once fired measurement - 2.270"
twice fired measurement - 2.272"
3rd firing & crush fit - 2.2725"
Total shoulder forward movement .0195"
So if you took the once fired case and moved the shoulder back to 2.268", it would have no real effect. Once you have the crush fit then move the shoulder back for easy chambering but I typically only move it .001" or so. Would move it only .0005" which would relieve the crush fit but due to variations in brass thickness, hardening and press linkages, .001" will assure chambering in a +- world
Now regular cases have a much tighter manufacturing tolerance in fitting your chamber because the manufacturers know the case should not be allowed to move too far forward in firing and blow the primer.
For example I'll pick one of my best shooting factory rifles without a custom chamber, even though it has more room than usual for "shoulder advancement"
Steyr 30-06 unmodified
new case measurement - CBTO 2.040"
once fired measurement - 2.0485"
twice fired measurement - 2.050"
3rd firing measurement - 2.051"
4th firing & crush fit - 2.0515"
Total shoulder forward movement .0115", which is just about the limit for movement without losing the primer and it does cause primer flattening even on loads not approaching maximum
Again no reason to push shoulder back until crush fit
Now the real danger is if someone took CBTO on a
new case and resized to that dimension every time, a case head separation would shortly occur and be dangerous.
The real question that goes beyond this reloading 101 (OK maybe 201) is - what causes the case to develop a crush fit at all? Since brass always springsback, hardened brass more than soft brass, how does the case ever develop a crush fit between the case-head/bolt face and the case-shoulder/chamber-shoulder interference fit?