I have been asked to do some load developement work on a 7mm RUM that has been fitted out with a new Leupold Mark 4 6.5-20x50mm LR/T M1 rifle scope. Now problems first started to show up when I zeroed in the rifle at 100 yards. I got the scope zeroed onto the aiming mark then loosened off the turret grub screw and set the elevation turret to zero. I then tightened the grub screw. First problem is that the turret is now very hard to rotate unless I back off the tension on the grub screw. Second problem is that when I back off the tension on the grub screw the point of aim changes. This I found strange. I held the rifle steady and looked through the scope as I loosened and tightened the grub screw. As I did this the cross hair moved about 3" at 100 yards on the target. What am I doing wrong? Is the scope faulty? It is suppose to be a new scope.