Since manufacturers have to stay within specs to saami and that means from min. to max , what about the chamber shoulder ?
Saami says .375" or 3/8 " in diameter , does this have to be exact or do they fudge this part too ?
A manufacturer takes the max liberty with these dimensions to get more life from the tooling. An accuracy gunsmith will specify the minimum size reamer. The .375" on the 30-06 is the datum diameter measurement. It is 1/2 way up the shoulder. From the bolt face to this dimension "head space" has to be spot on 2.0487" to 2.0587" or .010" long to be in Saami chamber spec. The .010" range on this measurement is not a range of where that is measured but the length of headspace. (bolt face to datum line) On a new chamber the difference between is measured with Go and No Go gauges. The difference between these two gauges is generally accepted to be .004" from min to max.
Min spec Saami reamers will be at minimum spec on all dimensions where a production grade reamer starts .010" big overall and leaves plenty of room for sharpening before it gets to min spec. This is how JGS explained it to me on the .010" oversize.