Good article by David Tubb on Ammunition Testing for competition.
New brass never shows the pressure once-fired brass does, so I shoot the initial tests with new brass. I start with five new cases and use those same five cases as things progress. When I seat the primers again after that first firing, I can easily tell the kind of pressure I have. A lot of people are measuring the case head and looking at the fired primer to see how flat it is and so on, but my gauge is the primer pocket. How well the new primer fits the pocket of a fired case is the acid test for me because it directly reflects on how much case-head expansion is occurring. This is why I fire the same cases over and over. Doing so lets me duplicate the fatigue I can expect in subsequent loadings.
