The majority of my doubles are Foxes. Snap caps are wasted money for them. Fox themselves wrote in their literature that their guns can be dry fired an unlimited amount with no damage whatsoever to any component, because of the one piece hammer/firing pin that is was/is built with a large boss that takes the blow of the fall. The striker hole can never be pushed out around it, and the striker itself will not break from it.
As for most other makes, I don't believe that the life of any of them that have strikers powered by coil springs will be extended by the use of snap caps. I do not dry fire them because of potential damage to striker holes in the standing breech, but just leave them cocked. I have my doubts about the leaf springs as well. All leaf springs are under a degree of flex, even with the hammers down, or they couldn't stay in place. I have removed too many of them to be told otherwise. The only issue is, how much flex causes their life to be shortened.
Not trying to talk anyone out of using snap caps. Just my reasons for not doing so.
SRH
