There is a long or several long threads on double groups. It usually is a bedding issue or something is loose. Is it a known performing scope?

I would be disappointed in a new barrel that still fouls after 100 rounds. I would contact Barrett about this. If not a new rifle I would do the finer grits from a Tubbs throat maintenance kit and then Dyna Bore Coat or whatever they are calling it now. A new semi custom should not need this.

As someone else posted I would just be concerned on the first three shots trying more only for load comparison. It could be something as simple as the bench set up and technique. Melvin Forbes had a recoil reducing bag set up that really helped shooting light rifles as it kept them from slidding backwards as much. Not sure these are still made.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli