“I purchased 2 boxes of ammo to break it in and begin the process of tuning a load for the rifle with the spent brass. I've read before how one member is adamant about checking the length of an unfired round before firing to provide a "measurement" if you will, of the effect the chamber has upon the casing. Well, the measurements were all over the place. From 1.623 to 1.64 prior to firing checked with a Hornady headspace comparator gauge”
That had to be me, I do not use the Hornady case comparator, I make comparators, I make chamber gages and my Wilson case gages are precision case length gages. You measured the length of the cases in 2 boxes of new ammo and found the length of the cases varied from 1.623 to 1.640, and I ask, how did you get the bolt to close on the case that was .017 thousandths longer than the shortest case. And you said the case length after firing was 1.624-1.6235.
The effect the chamber had on the case when fired, and I said that also, I have purchased new ammo, I have measured 20 R-P 30/06 rounds of ammo from the same box and found .001 thousandths difference in length from the case head to its shoulder/datum.
And I said I could determine the effect the chamber will have on the case when fired by determining the length of the chamber first. New, over the counter, unfired, factory ammo should be minimum length or = full length sized cases.
According to your measurements you started with new/minimum length size cases, according to your measurements your cases did not stretch when fired, according to SAAMI your chamber is .004 thousandths longer than your minimum length size cases but according to you, you measured new ammo, you chambered a case that is longer than a field reject gage and chambered it without felt bolt closing.
“But, all fall within .0005 of each other(1.624-1.6235(guessing at the .0005 as its halfway at least between the 3 and 4)”