Re: Case Neck Prep
"...how can you figure out what your chamber was machined to."
Mike a fired case neck and add 1 thou. The springback on most necks is so close to a thou that any slight difference won't matter. Or you could make a chamber cast to measure but it would only prove what a fired case will show you close enough.
Bullet tension typically varies by metal alloy and temper variations as much as any tiny thickness variations, and the temper - metal hardness - changes with every cycle enough you can feel it when you seat bullets, so precisely turning factory cases for a factory chamber is meaningless for most rifles. Most of us settle for skim turning enough to clean up something like 60-70% of the neck circumference and let it go at that. It's hard to see any accuracy difference attributable to neck turning alone, most of us who do it know we aren't helping much but it's something we can do to improve overall consistancy and doing it doesn't cost anything.