Diassemble a primer, or a few different ones. Actually take the battery cup out and check it with a magnet; you'l find most, or all current cups are steel. Up until recent years, (70s maybe) the battery cups were brass, and there were very few misfire problems, or primer dragging making hard opening of some guns without rebounding hammers. Today you have to experiment and find a primer/shell that is soft enough to fire reliably, and hard enough to not drag. From my experience, Fiocchi primers are hardest and cause most misfires in old guns not designed for them. I do not mean to bad-mouth Fiocchi, just state my experience. Try some old paper vintage shells and see how they perform.
