When you mention the variations in "length of the fired cases" with the Hornady Case Gauge, it sounds like you mean head-to-shoulder length, not overall case length. Is that correct?
"Only" .0015 inch bump of the shoulder is common with many FL dies--especially in improved cases, because so many chambers vary somewhat in headspace.
The best rule is to have unfired factory cases chamber slightly harder, due to the slight radius on the shoulder/neck. This prevents the case from being driven into the chamber very far from the impact of the firing pin, so fire-formed cases end up firmly headspacing on the shoulder.
This may not seem to be a big deal, but have seen .257 AI rifles with chambers set up correctly for this engagement of the new-brass shoulder/neck radius fail to fire around 1/3 of the time when using previously-fired brass. This is because the fired brass lacks that little radius.
John,
You're correct. It is the head-to-shoulder length I was referring to. The factory rounds did chamber very snuggly, so I was confident that there wasn't forward movement during firing. The factory rounds were 20 years old, so I was hoping the brass might be a little more consistent than more recent batches.
