I was always told not to dry fire any gun. But, I recently took a concealed weapons course and the instructor said we should practice not only at the range, but at home by dry firing the weapon (he said hundreds of times) to loosen it up and get used to the feel etc. Is it OK to repeatedly dry fire a revolver? An automatic?

Bet you get more attention in the "normal" pistols forum further down. I know it's fine on new rifles, but I'm not sure on revolvers or autos.

Not up on a lot of the new guns so can't answer for all of them.
I wil say that most of my practice in competetive years was from dry firing as was suggested to you. The S&W's,colt,glocks,berettas, can be safely dry fired. Any doubt contact the manufacturer.
Neal

Snap Caps are cheap and will give you peace of mind

Snap caps are fine, with or without them fire away with any center fire handgun. The only guns, semi or auto that should never be dry fired are rimfires.