The best way, if you are shooting SAMMI spec chamber and cartridges, is to look up on the SAMMI website and find your camber print. There will be two prints, one for the chamber and one for the cartridge. On the cartridge print you will find the max length, then look at the chamber print and it will show the distance to the 45 degree cut before the throat. That is generally 10 thousands but not always, sometimes more, sometimes less. So what you want to avoid is during firing, the neck stretching and hitting that 45 degree taper and pinching the neck down and creating a pressure spike. This can be more critical with a 20 degree shoulder vs a 30 degree or greater shoulder due to stretching of the brass. Bottom line, at the max trim length you will have plenty of room to spare, but you must pay more attention to your brass length, maintaining that trim length. Hope this helps?
6.5 creedmoor is 5 thousan. Top is cartridge, bottom is chamber. Like I said some are more some are less. Hope this clears up your confusion?not true
sammi is a lot more than 10 between chamber and case at the neck length.
the trim spec is 10 but the actual distance is much more