Since I live and hunt at times in the desert imo heated ammo, rifles and outside temps can make differences in how heated ammo left in the sun or in a heated rifle increase pressures. IMO how a person re-loads, re-loading practices, components used can change how powders react. I'm not so sure I could replicate what you did. Where I would most likely start if I were going to do this test would be to have 2 different brands of 6.5 creedmoor test rifles, different types of stocks, using the same handloads, side by side targets , under the same conditions and rotate shooting one rifle then the next to lessen any outside influences . The cheap way go find a friend with a different kind of Creedmoor and go shoot them and see if there is a difference. Another idea borrow a digital thermometer hand held tester and aim it at the receiver then end of each barrel, 2 temp readings per shot per rifle and write the test reading down on paper. Keeping track /record of the target shots on paper for later reference. Then I could have a better understanding of what's going on. If both rifle's pulled the shots downward the same amount as in your picture then I would have some questions, same thing if using 2 of the exact same rifles with the same bedding pressures, etc. possibly changing bedding pressures and see if it makes a difference. There's so many things to cause these bullet drops you would almost need a process of elimination to be sure, It's interesting to talk about, not something I going to go out any try.