We just went through this. Oh, well.
Okay: Modern revolvers and semi-autos are not harmed by dry firing, generally. Overall, if you are going to do a lot of dry-fire training, you're better off using a "snap cap".
Same for rifles and shotguns. Snap caps are cheap insurance, whether they are "needed" or not.
Don't dry fire revolvers whose hammer has an integral firing pin, such as the Colt SAA.
I rather doubt you could hurt any revolver which uses the Ruger-style transfer bar system. (Well, I've never been able to--or a Govt model Colt, either.)
FWIW, Art