Were the rest of your groups shot from a hot barrel? If you have any kind of stock to barrel pressure especially as the barrel gets hotter itll throw some bad groups. The first group being cold barrel pressure wouldnt be near as bad. See if you can slide a dollar bill betyween barrel and stock from the front of the fore-end to the recoil lug. Make sure your action screws through the stock are torqued right and one of them isnt causing pressure. After that maybe try another scope.