I've been working up a load for my .280R, started with 50grains RL-19 (160gr NA), and worked up to 53 grains. Of 8 rounds fired (53gr), about half showed very slight flattening of the primers, with the associated rim on the cup when I de-primed.
What would account for this difference between the same loads?
I was very fastidious when it came to measuring my powder, so I am confident that I was as accurate as could be with a standard scale.
Also, I am not yet using a chronograph, as I am more concerned with whats shooting well out of my rifle, and have no pressure signs. Is not using the chrony handicapping me in terms of not having the complete picture?