Any snap cap that becomes permanently deformed by the firing pin will then fail to do it's job. Seems to me that a spring loaded snap cap with the striking surface being something that will not become permanently deformed while at the same time providing as soft a surface as possible would be the way to go as long as it has the correct spring backing it up.
I'm of the opinion that most guns can be dry fired without causing any damage. The only time dry firing becomes a problem is when the fit of the firing pin in the breach lock is such that contact between the two occurs too close to the pin itself. You can check your gun's contact area by disassembling it, thoroughly cleaning both the breach lock and the firing pin, and then brushing on a very thin coating of Prussian Blue on the front of the pin. Then load the pin in to the breach lock and press it in firmly with your finger. Then remove it and look for witness marks to see where the pin is contacting the breach lock. If the contact area is sufficiently far enough away from the small pin, you're good to go.
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