"I wonder if "don't dry fire" is even older than cartridge guns. I would think dropping a hammer on a percussion cap nipple wouldn't be good for it."
Quite correct. I've seen more than a few percussion guns with nipples smashed flat from dry firing.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.