For function testing a gun (triggers, ejectors, etc.) they are indespensable. I guess I could see where excessively heavy versions may (over time) unduely strain ejectors, but IMHO, that would take some fairly excessive use. A problem I have encountered with snap caps is where the primer pocket isn't beveled adequately. On some guns, (the two that come to mind were an LC Smith 3E and a Stephen Grant toplever sidelock) this can cause the firing pins to hang up or stick in the cap, effectively rendering the gun un-openable and necessatating a trip to the gunsmith to have the lockplates removed in order to unstick the strikers. Needless to say, that particular pair of caps was disposed of, forthwith. These weren't inexpensive versions either, they were chrome plated and otherwise well-made.
