Won't hurt a thing if its a quality firearm. Even quality rimfires have a firing pin stop in them to keep the pin from contacting the breech face.

Only gun that I ever harmed by dryfiring was a yugo mauser- dry firing the rifle twice caused the shoulder on the firing pin to be peened back and the safety no longer would work. The rifle was probably unsafe to shoot in the first place- the receiver is very soft, and workmanship on quality on the rifle is very poor.