Rich,
I'll let you make up your own mind about snap caps or not. They sure dont hurt anything, but.....
I have personally dry fired multiple thousands of times over the past about 50 years. The revolver I dry fired the most was an early Model 19, which I carried and also fired multiple thousands of times during the late 60's, 70's, and 80's. I also dry fired some Model 10's quite a lot during those years. I was present when Model 10's and Model 15's and other Model 19's and 28's were dry fired during annual Police Academy Trainings during many of those years. As an instructor, I loaded up several sets of 18 dummy rounds with spent primers, no powder, and full wadcutter lead bullets. We carried our spare ammo in 12 loop belt slides, so we had 18 rounds immediately at hand. Loading from the belt slide was the only way we allowed recruits to load during the PPC qualification training. These dummy rounds were discolored so as not to get them mixed up with any live rounds! During training time over a couple weeks during the Academy, individual recruits who were struggling with reloading and firing to meet the required times for qualification would be given some extra tutorial training at night after supper to help them gain the skills they needed. These dummy rounds would allow me and usually another instructor or two to spend some time with three or four students and practice firing and reloading the 12 rounds in the loops under stopwatch times. We had pretty good luck doing this for those who needed the help, but the revolvers we used for this were fired thousands of times with these dummy loads. The spent primers provided little if any resistance to or support for the firing pins.
I also recommended dry firing to other officers who struggled at quarterly qualification times in the District where I worked and was assigned Range Master duty.
I've said all that to say this. I have personally never seen damage to an S&W revolver beyond normal wear and tear that could be traced directly to dry firing. Not saying that it can not or does not happen, but I just never saw it happen. We did sometimes have problems with the highly used revolvers used during training that sometimes required the attention of the Dept. Armorer, but I was never aware of firing pin problems or damage caused by dry firing. Those old guns pretty much went bang when you pulled the trigger unless the low bid contracted practice ammo was not high quality. We had numerous squid loads and lockups at times when primers didn't light up at all or when a round did not had powder in it. It's hard to get a student to stop firing when you are standing next to him or her and that student is pulling the trigger as hard and fast as possible to make time! We had a few times when a couple of bullets would be driven out of a barrel but mostly the bullets didn't get into the forcing cone far enough to allow the cylinder to turn.
What skill I had at firing well and quickly was the result of many hours at regular times dry firing my carry gun. As you might guess, the action on that old Model 19 was pretty slick and smooth from all that dry firing! I still today say that if you are going to use snap caps, you should incorporate reloading when you have "fired" six (or five) "shots (alla y'all do count your shots, don't you? It's not a bad habit to develop when you are not under real stress!). Reload using whatever method you have chosen to carry your spare ammo. Remember that perfect practice makes perfect. A bad habit is just as easily learned as a good one, but it's mighty hard to break a bad habit that is well learned!
I just relate this story for whatever it might be worth to anyone reading it. Again, I'm not trying to tell you what to do, just relating my own experiences that began back in a day and time when things were not nearly as sophisticated as they are today. After all, we used to stick empty brass or a wad of cotton in our ears to try to keep our ears from ringing all night long after a long day on the range. Sadly, we didn't have much access to good ear protection in those days. What's that you say?
