At the bottom of page 17 in the Instruction Manual foir the Ruger SR22 we find:Rim fire guns must NOT be dry fired.
Bottom line: Some actions can be dry fired. Some should not be dry fired.Going through the actions of cocking, aiming and pulling the trigger on an unloaded gun is known as “dry firing.” Dry firing can be useful to learn the “feel” of your pistol. Be certain that the pistol is fully unloaded (both the chamber and magazine are empty) and that the pistol is pointing in a safe direction at all times, even whenyou are practicing dry firing.The RUGER ® SR22 ® pistols can be dry-fired without damage to the firing pin or other components as long as the magazine is inserted.
Thanks.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