First thing I checked was the parallax and scope mounts.There was an older guy I knew,had a tiki 22-250. His eyes were really bad an we had the scope set for his eyes. I couldn't hit nothing with that gun. He past away a few years ago, his grandson adjusted scope to his eyes, guess what, we both can shoot it well now. Maybe not your problem, but might be worth checking your scope an adjust it.
I would agree with the shooter issue but I'm not a novice, I'm not a competitor but I shoot more in one week than most in a year. Thousands of rds a year through many guns and I've never seen this. I also know everyone can have a bad day but I just shot the 100 groups an hour earlier. Stability I guess is a possibility but how would unstable bullets shoot consistent 1/2 or less at 100?
Not enough spin, the bullet slows down, and just like a gyroscope the bullet starts to wobble.
I know a guy who burnt one up in 200 and one in 400 in a 26. A barrel with that kind of erosion your gonna be constantly chasing your optimal seating depth.I have a buddy that cooked a couple 26 Nosler barrels after a couple hundred rounds.
Was talking more on eye piece at beginning of scope.First thing I checked was the parallax and scope mounts.