Re: Vertical stringing=optics problem?
Culprit found, I think.
Looking at everything for the 7th or 8th time, I noticed that the back of the rear ring was about 1/16" above the base. Tried jiggling it, but nothing moved. I loosened the screws that hold the rings to the base and found that the little ears the screws capture had been bent down and back. This allowed the ring to cant slightly forward, raising the rear of the scope, and the Pos-Align inserts let it do that without binding on the scope tube.
The Burris standard ring attachment method seems to rely on the front dovetail to provide the support against recoil, with the rear just centered by screws and not load-bearing. Apparently, the front ring with the plastic Pos-Align inserts couldn't clamp the scope tightly enough to keep it from moving forward a bit under recoil, and the back ring just pulled a bit more out of it's mount every shot or two as the scope moved forward.
Does this seem like a reasonable scenario? Any suggestions for a more secure setup?
There is no "overkill". There is only "open fire" and "I need to reload."