the ruger mark3 isnt that hard and easier than most 22 semi auto to tear down and put together. the instruction manual has an exact step by step and the folks that have trouble with em are the ones that dont read the manual
the only part that sometimes folks have a hard time grasping is the hammer has to be in the cocked position to put the bolt in and then moved to the fired position once the bolt is in to put the mainspring housing in.
to do that you pull the trigger and tilt the gun muzzle up hammer falls to to the cocked position. slide the bolt in then pull the trigger tilt the muzzle down hammer moves tot he fired position and you can install the mainspring housing.
its really not that difficult once you understand why your doing what your doing.