IMHO, assuming that the scope is NOT the issue and you have not shot out the rifling, then the ring holding the scope to the mount may not be too tight or the mount is not firmly installed or the barrel is no longer free floating. Since you did not mention getting a new scope ring, why not invest in a new rings and really use blue loctite on them to secure the mount and the rings tight. You should not be dropping a foot for making 4 click adjustment ( 1 inch typically )
Finally, give the barrel a good cleaning, making sure to remove lead and copper deposits.
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