B. Bart, your correct about the benchresters full length sizing. The benchrest people are utilizing very close tolerance (Minimum SAMMI) chambers that require neck turning inside and out. there necks don't expand .001 upon firing If the have and action with a spring button ejector they remove it or weaken it considerably. In a factory chamber the extractor button actually can push the cartridge to one side for possible misaligment in the chanber neck. note I said possible, not definite
Headspace gauges reference from the bolt face to the shoulder datum line not the neck. A 06 headspace gauge is used for all calibers from the 25-06 up to the 35 Whelen.
If you have time to do it twice, then you have time to do it once right and put your name on it