The only thing I can think of that would explain it, is that a bullet can take 100+ yards for the gyroscopic precession to dampen out, which causes the bullet to rotate about its axis of travel. If three bullets hit a target at 100 yards, and all three were at opposite positions in their rotational precession range, you'd get larger groups than after the precession is dampened out and the bullets are hitting very close to their center axis of travel.
But, Bryan Litz has said that so far with his shoot-through target challenge, nobody has reported larger groups at closer range than the groups the same bullets print at longer ranges, and that group size is proportional with distance, so that's it. Form is right.
The only explanation at this point is that group size at closer range exceeding group size at longer range is caused by random variation in the precision of the load, and nothing more. If you shot 50 groups at 100 yards, and 50 at 200 yards, the average group size should be proportional to distance, but if you look at only 1 or 2 isolated groups at each distance, you might see smaller groups at 200 yards if they were exceptionally small 200 yard groups and exceptionally large 100 yard groups.
