It had to be something internal. The scope was installed by a master gunsmith in my area. The bases were tight as was the front dovetail and rear elevation screw. And the tube was crystal clear. And it was a shame because it was very easy to acquire a target which surprised me. But that is probably also do to the fact that the stock fits me well. Now I have to go down to him and get 4 plug screws to fill the holes.