vic479h, Ruger owner manuals are your friend .... in this case Ruger specifically says it's OK to dry fire any Mark Series pistol. Why? When the Standard and MK I were in production, they did not have an auto lock-back bolt so what you did was to keep firing until you hear a click-no bang. This meant you dry fired at least 10% of the time. In order to prevent the firing pin from damaging the chamber mouth, the firing pin was designed with a limit pin that prevents the firing pin from traveling too far. This pin is called a "firing pin stop" and has been included in all Mark Series pistols from day one. Ruger used a solid steel pin until the MK IIIs ... then it was a hollow roll pin. These were problematic because they often broke. Ruger is back to using a solid steel firing pin stop.
If you dry fire excessively, the firing pin stop pin will eventually bend and allow the firing pin to travel beyond the limit. Replacing a bent stop pin is very easy and cheap so if you dry fire a lot, inspect the firing pin stop pin every time you field strip for cleaning and replace as necessary.
The firing pin stop is part # 16 in this schematic:
http://www.brownells.com/schematics/Ruger-/Mark-II-22-Standard-Target-sid12.aspx#s29033sid12