Browning BBR in 7mag not grouping

I am working on a BBR in 7 Rem mag that is doing the same thing as the other posters 06. I have bedded the action,used Sweets to get out the copper fouling (there was alot), crown is good,swapped scopes,tried different ammo,and the groups still are all over the place, and run 6-8" @100 yds. with flyers. I noticed the cases are swelling about .006-.008 over a new shell-oversize chamber not centering the shell? The rifle was bought used,and would do 1 1/2" groups. The owner said he never cleaned it more than running a brush through it every now and again-I could tell by the verdigris at the muzzle. Any other suggestions? I am leaning towards setting the barrel back or a new barrel. Could save time and tell him to buy a new gun.