several things can cause that...wind would be one but im betting its you laying on the rifle different from group to group(canting the rifle differently) or maybe a little flinch from the 7mm?...shooting off bags wont stop pulled shots,flinch,slapping the trigger ECT...next time you go out shoot the 280 first and when shooting REALLY pay attention to trigger pull and follow through and also if your doing something wrong or different from shot to shot...9 times outta 10 you can figure out what your doing if you really pay attention.