Just had my Ruger Mark IV .22 pistol converted to a dual semi auto and single shot that makes my suppressor about 5-10 decibels more quiet. It has a fire control selector Titanium knob installed in the regular Ruger bolt. By turning the selector knob 90 degrees it locks the bolt operation making it a single shot pistol which results in a higher velocity of the bullet and reduces the noise of the cycling bolt and escaping gas.
It looks neat, easy to operate and when firing in my integral suppressed Mark IV, is much quieter. I also add one to Ruger Lite 22/45.
In cooperation with my nephew (an 07 licensed firearm manufacturer and master machinist) we designed the bolt lock to fit the Mark I, II, III & IV pistols. They are CNC machined in Ohio and installed in the pistol after machining a locking groove inside the rear of the receiver. You can see the bolt conversion on GunBroker under "Ruger Mk I, II, III, IV Conversion Bolt - Semi Auto/Single Shot".
I just purchased a new chronograph set up (delivered this week) to better check the ballistics in semiauto vs the single shot mode but weather has prevented the test. Also have a newer sound meter on the way to better record decibel levels between the firing modes. Thanks for the reply.