There is a difference between a gun that is loose and one that is off te face.Some guns are "loose or slack in the boby from the day they were made but rely on the forend to keep them tightand when the bolt closes they are fully sound. A gun that is slack in the bites is a lot worse as the wear rate will increase rapidly.
As to all this about shims ,why not just put a new joint pin in ,if its removeable?