What Oldgungeezer said. I know people routinely dry fire, sometime thousands of times, without snap caps, or something to cushion the hammer. But I'm not going to beat up any of my guns doing it. Once bought a pristine model 19 that showed very little evidence of ever having been fired at all. But firing pin bushing was beat out of shape, and enlarged by dry firing. Firing .357 would cause primer flow into the enlarged firing pin bushing, tieing up the gun. I sent it back to S&W for a new hammer nose bushing. Was at Gunsite. Friend shooting a S&W he'd dry fired a lot. Firing pin broke during the training.
If I dry fire a gun, I use snap caps or something to cushion the hammer fall.....YMMV