I figured out what at least part of the problem was with that .260 I was shooting last week. Went to take the scope off and discovered that the rear base screw was stripped out! The base would move up to 1/8" depending on if it was propped up on what was left of the thread or flush with the receiver. I drilled it out and tapped it for a #8 rather than the stock #6. Should be getting my new scope in today and I hope to test it out again this weekend. No wonder we were seeing those huge and strange groups with the ladder test! It's a wonder I even got every round on paper!
Glad to hear you were able to remedy it. Let us know how the new scope works out for you.