In the comments section of this post, there was a bit of discussion about dry-firing. One of the participants, Og, expanded on his views on his own blog:
I'll focus mainly on pistols here, and note that a lot of older deigns (and by older, I mean pre-WWII) may not be particularly amenable to dry-firing; ditto for most rimfires. Others, most notoriously the CZ-52, have issues with the quality of the materials used. It is, however, my considered opinion that the dangers of dry-firing to a modern centerfire firearm in serviceable order are vastly overblown.
In the field of revolvers, there is a subset of the conventional wisdom which states that older S&W revolvers, with their floating firing pins riveted to the hammer, will break when dry fired. If the pin is prevented from floating and is trapped in its downwardmost position by rust or gunk, then this is a possibility. I will also state that in all the untold thousands of job tickets for busted firearms I filled out between 1993 and 2007, exactly four were for broken firing pins on S&W revolvers. I have a few that have been dry-fired many, many thousands of times.
As a matter of fact, my daily routine over a period of several years was to dry-fire my pocket J-frame, at first a 442 and then a 432, fifty times as rapidly as possible with each hand and then, while my fingers were good and worn out, try to hold the dot from the laser steady on the backstop through the normal double action pull. Now, both these guns had the newer frame-mounted firing pin, but still... Call that 150 dry snaps a night, pretty much every night, for a five year stretch, and you have a wheelgun that has been dry-fired well over a hundred thousand times. Last time I was under the sideplate, nothing was out of sorts, although I'll note that the bearing surfaces of the lockwork were shiny.
Similarly, I couldn't tell you how many times my two current carry 1911s have been dry-fired, except to note that I religiously replace the firing pin springs whenever I replace the recoil springs.
But in the end, my experiences are merely anecdotal. And I certainly wouldn't dry-fire another person's weapon, unless given permission, because other people obviously hold differing opinions on the topic.