I'm about to start using bushing dies for the first time though I have years' of experience of the non-bushing type. I want to be sure I've got the workflow clear in my mind.
This is what my Sinclair catalogue says on the Redding page about "Determining Redding Bushing Size":
"The proper bushing size can be easily determined by measuring the outside neck diameter of your loaded cartridges with a precision micrometer or dial caliper . Then, simply subtract .001" from the cartridge that has the smallest average neck diameter. This diameter bushing will generally size case necks just enough to create the proper press fit for the bullet."
Question 1: the mandrel which carries the decapping pin is smaller diameter than the case neck which tells me that the mandrel is not designed to support the inside of the case neck whilst it is being compressed by the die but is there simply as a carrier for the decapping pin. Beyond that it plays no part in the resiizing process: yes?
Question 2: Is it more worthwhile to take the measurement on new cases or on cases which have been fired through the rifle?
Bearing in mind that this is a factory rifle with a factory chamber, I don't expect to be dealing with a "tight neck" chamber where clearances between chamber and case neck are critical.
Question 3: The instruction reprinted above in italics: it doesn't seem to acknowledge that the "loaded rifle cartridge" could have been loaded with more or less neck tension in the first place. So, if we're starting from a random place, surely all the bushing die is doing is creating repeatability of that randomly acheived neck tension.