Adding A Pre-Travel screwBack to Ruger MKII StuffPart numbers and names referenced in these instructions can be found here First field strip the pistol then remove the trigger from the frame. This information was origonaly posted in the Mark II 22/45 Forum by Bullseye quote: 
There's really not much to it. You just get a 4-40, "3/16" inch long Allen screw and tap the trigger mid way between the pin through hole and the bottom of the trigger's front face with a size 4-40 tap. I tapped mine with a #43 twist drill (a #42 will work also, but give you less metal for the threads). You can also can use 6/32 x 3/16 screw with a 6/32 tap and a 7/64 drill but be carefull not to get into the trigger axis pin hole area. The Pre-travel must be installed below the trigger through pin hole. A screw installed above the trigger pin through hole will adjust the over-travel, this is the screw that the factory target trigger has installed in it. The screw can be adjusted to take the slack out of the trigger before it engages the sear. This will shorten the Mark II's trigger pull considerably. You will need a little bit of slack (only a very little) to leave room for the disconnector to reset during sustained fire operations. The trigger will not operate repeatedly if its not there. The pre-travel screw can be a pain to adjust because you'll have to completely remove the trigger to do it. However, once you get it adjusted correctly the feel is worth the wait. I used a little blue locktite to keep the screw from moving by recoil. The screw uses the trigger slot face as the primary surface for the adjustment and will keep the trigger from returning all the way back to the forward most position. Good luck. R, Bullseye Posted on Mar 9, 2003, 10:42 PM This information can also be applied to adding a Pretravel screw to a factory trigger also. Which may have an over travel screw in a similar location in the trigger, only above the trigger axis pin. Here is a pic of 2 triggers with the factory over travel screw (above the trigger axis pin hole) and a pretravel stop installed (under the trigger axis pin hole): 
And here is another way to do it. The advantage of this method, is that you can adjust it without breaking down the pistol, but the dissadvantage is that you are modifying the frame, and if you mess up, it could be expensive to fix. A trigger is much easier to replace. (also my frame is stainless, which is harder to work with than the aluminum trigger) 
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