Dry firing any weapon will mess up the firing pin/spring assembly sooner or later. Get yourself a "Snap Cap" in the appropriate guage. These can be bought from most larget retailers or from MidwayUSA. Regards, Mikey.
I've made snap caps in several calibers/ gauges by filling the primer pocket w/G.E. Silicone Sealant. After curing 24 hours I trim it flush w/base of case/shell. You can also load the case with shot or slugs to make the dummy round weigh 'right'.