Re: Flattened Primers
I used to get the flattened primers all the time, same as you, no craters just flattened.
I just accepted it, I had no other pressure signs at all. If accuracy was good, I used the load. I switched to neck sizing dies, and honestly couldn't see any improvements in accuracy or the primer issue.
I then heard a target shooter talking about reloading, and he spoke about neck sizing, should/can only be done 1-2 times before full length resizing, because as the brass flows to the shoulder area, neck sizing only will start to allow the shoulder to require jamming on bolt closure. This causes inconsistent neck tensions and hurts accuracy. Something I had noticed, after a few loadings the groups would start to open up.
So I searched online for a Headspace Gauge, that could be used for multiple calibers, and found this one.
I couldn't be happier with the gauge, you simply measure the shoulder of a fired case, and adjust your full length die until you are bumping the shoulder back the desired amount. (.001")
This insures you are sizing your brass to your chamber.
Improper head spacing the way I understand anyways allows the case to move forward to contact at the shoulder when the firing pin strikes, then there is room between the case and the bolt face, which as the powder ignites the primer actually pushes out of the case to contact the bolt face before the brass stretches to take up the gap, which crushed the primer. This is one of the causes of flat primers, even without too much pressure.