Amathis, “On the first round the primer looked a bit flattened and had worked out a bit” and then “primers do some strange things” When primers work out ‘a bit’ the reloader should look the other way as in the opposite of looking for pressure signs and start looking for the lack of pressure signs. I have not seen the cute little demonstration/illustration/cartoon that is believed to explain, to the reloader, everything they would ever need to know about the sequence of events after pulling the trigger, the firing pin jumps out, chases down the primer, after catching the primer (after the case shoulder hits the shoulder of the chamber etc., etc..) the firing pin strikes the primer and then things pick up, it is believed, anyhow in that sequence of events the case and primer are forward of the bolt face, by design the case head must finish against the bolt face, if the primer is ‘worked out a bit’ it can only be said the primer made it back to the bolt face but the case head did not.
When the primer backs out it looses the support of the primer pocket, then there is time, time is a factor.
That's exactly what we determined after running the numbers. An additional sign was that there was soot on the case neck meaning there wasn't enough of a seal. We figured the lack of pressure was not forcing the round back against the bolt face. As soon as we have some nice clear weather and the Chrony will cooperate, we're going to run some higher loads.
My original post was to clarify that primers can flatten in numerous situations not just over pressure. Reloading reminds me of the slogan of the board game Othello: A minute to learn, but a lifetime to master. Reloading is an easy thing to learn, but to learn the intricacies of a firearm, and to know exactly what caused what takes a lifetime.