There should be a list of things to check, probably already in one of the Gun Gack books. I will mount the scope on another rifle or use a known scope to re-test. I suspect sometimes when I have done this I corrected an unknown mounting issue when making the swap, especially if I put the original scope back on and the problem is resolved.

If nothing is loose (or overly tight) and there is no barrel contact then it gets more difficult to diagnose. How is the crown on the barrel?

Also try different ammunition just to eliminate another variable. How many rounds have you fired? I have had some barrels start shooting better after 100 or more rounds and cleaning.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli