Found the forum i was referencing…..
Sometimes the brand of brass comes into play. If you look at the SAAMI drawings for the diameter of the case extractor groove, it shows as "0.409 -20", so 0.389-0.409. The vast majority of brass that I have in my reloading stash - Lapua, Federal, Remington, Winchester, Norma, etc. measure between 0.403 and 0.406, across all brands. Except Hornady. The Hornady 6.5CM brass I had meaured between 0.391, and 0.397 - so technically within SAAMI spec. But in my testing... under 0.393", and it wouldn't eject, but drop just like the OP described (which is why I asked @spudgun if he was using Hornady brass). Every time. Over 0.395", it ejected reliably. In between... maybe yes, maybe no, depending on how you stroked the bolt and if you were just lucky or not.
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The above quote was found in the below reference…..