I had a Browning BAR1 in 30-06.

MudderChuck got my most probable cause that could do what you describe - Crown damage. Yet U say no.
Next would be scope rings or the mounts were damaged - Would think between both GSs they would surely have found this problem.
Try an box of 180 Rem CoreLokts and post target. May want to reduce range and increase target size if really 4 foot groups???