The weak point in all the Marks, from the Mark II onwards, is the heavy and sloppy trigger pull. A 5 - 6 lb. trigger pull is simply unacceptable in a target pistol. There are a number of modifications that can be made to the Mark IV, that I have posted about before. Mainly, you need to get rid of the magazine disconnector. Substitute a simple Mark II style hammer, a Volquartsen target sear, and a Clark trigger, and you are good to go. To give Ruger credit, they have maintained backswards compatibility in the Mark IV.