Multi task-ers? Head space is ‘THE LENGTH OF THE CHAMBER’ from the bolt face to the shoulder of the chamber, the length of the chamber from the bolt face to the shoulder is the only useful information I find useful.
Again, I have a chamber that has an additional .016” added between the bolt face and the shoulder of the chamber, if I took the case lengthens serious knowing the chamber is longer by .016” than specifications/ammo manufacturing standards I would have a neck that is .016” too short to cover the chamber at the neck, meaning I add .016” to the case length because! the HEAD SPACE ‘chamber length is beyond field reject length’.
Then there are ‘us’ case formers, we neck up 30 cal cases to 35 cal or 338 cal. not fair, our case necks do not get thicker and or thinner when necking up or down, for the most part the necks get longer and or shorter when necking up and or down. POINT: When necking a 30/06 to 35 Whelen the neck shortens .030”, moving to 30 Gibbs, neck up to 338 then neck down to 30 cal while forming a new (2nd) shoulder, that is neck up then neck down, still the case is shorter by .030”, when measuring case length after firing the case former is never surprised the case shortens as much as .040” again, the part of the chamber that is not covered with the case is a concern for me. Moving on, the 280 Remington case is longer from the case head to the shoulder of the chamber .051” than the 30/06. Rational, it has been suggested the 300 Win Mag had a short neck, the neck of the 30 Gibbs is .217” long, that is shorten than the 300 Win mag. By using the 280 Remington case the reloader can gain case length, an increase in case length increases bullet hold and the longer neck covers more of the chamber exposing less of the chamber to hot, high pressure, metal cutting gas.
To understand is to be a multi task-er.
For all the rest there is maximum case length and trim to length with total disregard for all other information.