Welcome to the site. I believe you're explaining about a fowled barrel for the accuracy. I have heard of fowled VS clean barrel but that is a little extreme. That far off from the rest of the group sounds like a lot. Still all rifles are different.

I really do not know what to tell you. I have a few rifles that are a little bit off on fowled VS clean, but nothing as drastic as you describe. If you get a chance, try this.. load the rifle on a clean barrel and then take a patch and put a small amount of bore butter on it, and swab down to the projectile and then shoot it. See if that does not bring the shot into the group. I have heard of it working for others. Whether it will work for you, who knows, but it is worth a try.