"This whole thread is about "Feel good" extra work. I remember a '17 Enfield that after resizeing the brass it had gained about an average of .020-.025 in length. That is because military chambers are different. At 100 yards it......"
It is not my job to make you feel good, I will say had you put more extra work into your effort you would not have made the same wild guesstimate of a conclusion. You did not measure the cases before you fired the cases, do not feel lonely, that is a common practice with loaders.
You did not check the length of the chamber before you fired, again, a common bad habit among reloaders, you did/do not know the effect the chamber had/has on a case when fired, me? I determine head space first, then form, then fire. Without knowing the difference in length between the case from the head of the case to its shoulder and the length of the chamber from the bolt face to the shoulder of the chamber, you do not know if the length of the case increased from the head of the case to its shoulder, point being?
When sizing reloaders believe they are bumping as in "I bump my shoulder back etc.,etc.. and it is beyond their comprehensions when forming/sizing part of the shoulder becomes part of the neck and part of the case body become part of the shoulder, the shoulder did/does not move, the shoulder is still there where it was when the case was fired, the difference? the die forms another shoulder.
So, when you sized the fired cases the length increases when the new neck was formed, again, because the neck did not move and when sizing the shoulder is not bumped, a better term would be 'wreck' as in change.
And the Military chamber is different?