Yup, yet another question from "moi".
The SHORT version: Can hard crimp cause flattened primers?
The Full version:
Yesterday I went to the range and fired a couple hundred reloaded cases, .357 Mag. There was neither any unusual recoil, nor problem with extraction or anything like that. (shot from a revolver). Actually, I felt hose were my best rounds yet, as far as performance, uniformity, and appearance.
I just took my brass out of the tumbler and started sorting it out by manufacturer and primer used, and noticed that one batch had flattened primers on majority of the cases. I used Winchester Small Pistol Magnum primers on that particular round. Primer pockets were cleaned before seating (I am making that a habit). The charge was 8.9 grain Unique behind 125 grain copper plated FP. The max charge per manufacturer is 9.0, but I found some Lee data for lead bullet of same type that uses more powder, and plenty jacketed data that use even more. I made the OAL 1.580 instead of the 1.570 which should have, if anything, decreased pressure.
The strange thing is that I made the same round, but with 8.5 gr Unique, using CCI Small pistol primers, and those are nice and round, not flat at all.
OAL and crimp (Lee seating die) were exactly the same on both charges.
So, since I know it is not the powder charge or the seating depth, I am questioning whether I crimped too much. I might have gone too hard on the crimp, but I wanted to use these rounds in my Marlin lever and did not want them to move under recoil. The bullets have no crimp groove.
I set my Lee die screwing it in all the way on an empty case at full stop, until it touches the case, then turn in extra 1/2 turn. Too much?