For exposed hammer pistols, lever rifles and some revolvers, I roll a foam earplug up and stuff it into the receiver/slide/frame between the hammer and firing pin. Cushions the blow of the hammer when dry firing. Makes it slightly safer, and saves on wear and tear. They are cheap, too.
Andy

That's a simple idea. Have you had any problem with the hammer being blocked back far enough that you can't cock a revolver again without removing that cushion?

Not that I remember, but you can vary the amount of cushion by moving some of the foam above the hammer/frame.
Andy

I've used something like this before to save on the wear and tear....worked fine for me. Good call Andy