[T. O'Heir]

"...its brittle firing pins..." The FP isn't brittle. What happens is the FP gets whacked into the edge of the chamber and can peen that edge. Peening that edge means the chamber is damaged and won't allow the cartridge to feed. It has nothing to do with reliability or performance. And there is no number.
Using a snap cap will help. And it still depends on what rifle. Ruger, Henry and Browning say dry firing won't hurt their rifles/handguns. Smith says don't. So does Anschutz.