+1 what Cheesewhiz said. I don't use dry firing as a means to "smooth" the trigger group. For me, dry firing is a means of training for trigger control and thus is a slow deliberate process (which may also include drawing from concealment). With the SR-9 you actually do not have to rack the slide the full length of it's travel to get the trigger to reset - thus you can just keep one snap cap in place (along with the mag of course) if you like... Just pull the slide back perhaps half an inch or until you feel the trigger reset and you are good to go again... I like snap caps and I use them in every gun I have whenever I dry fire...
There have been a least a couple of reports of the striker assembly breaking when dry firing the SR-9. Search this sight or the other Ruger forum for pictures and details.