Does it really matter? Thinking more about this does it matter? Like most I have certain rifles I just enjoy shooting. One such rifle is a 308 bolt gun I built as part of a class maybe 25 years ago. The action wes trued and my barrel was trued. My finishing reamer cut was done using a Clymer pull through 308 finishing reamer. The finished chamber headspace was 1.632". I have checked the headspace over the years several times using a set of Forrester 308 headspace gauges pictured below. Years ago when I first bought these gauges I dragged them to work and checked them using an optical comparator and more recently these gauges were checked using a Zeiss CMM (Coordinate Measuring Machine).
Following firing, the brass in this rifle comes out right around 1.631" which would be my chamber minus 0.001". The rifle is heavy barrel having a 26" barrel length. My best groups with this rifle were right around 0.350" with 168 grain Sierra bullets. All of which is here nor there. All that matters to most average shooters is group size and the groups I mentioned were 5 shot groups at 100 yards.
New Federal Gold Match brass comes in around 1.629", I resize all brass for this rifle to a nominal 1.630" as using the RCBS Micrometer after checking it with my headspace gauges.
So looking at all of this, even discounting extractor clearance, the worst case scenario is my case head can only, at maximum be 0.002" away from my bolt face and the bolt face was lapped when I built the rifle. Even that opens another can of worms as how true a bolt face actually is in any given rifle? How flat is flat?
Finally how much does any of this really matter?
Ron