Not to argue with the Ruger factory manuals, but it is not a good idea to dry fire on most rimfires. Problem is, being a rimfire, the firing pin strikes the brass cartridge rim, cushioning the firing pin, and firing the weapon. Without the cartridge there, the firing pin hits the steel part of the chamber where the case rim would normally be. Over time, it can break the firing pin, and damage the chamber from the peening of the steel firing pin on bare steel. Dry firing is usually not an issue on centerfires, as the firing pin does not strike anything, and stops at the end of its travel without any undue stress.
Larry