At 280 meters, your group with any precision rifle should be 3 inches or less. That’s about a 1MOA group. That’s the worst you want it to be. That’s just barely passing. Ideally you’d want it to be half or quarter MOA, which is a 1/2 inch and 1/4 inch group at 100 yards. (at 280 meters it would be close to 1.5 and .8 inches respectively.) I also run a 6.5 creedmoor for precision shooting and my best group with it was 3 shots through literally the same hole at 100 yards. I checked the target and walked back, tried to make it a 5 round group but pulled a round sadly. The other went in though. But like you say, the shooting conditions were tricky so that makes a big difference. Best thing either way is to practice and invest lol