Rule303,
Have you by chance tried any of the 50m groups with open sights?
Does your first shot happen to be the most accurate of your groups?
The only experience I have had with vertical stringing on a scoped rifle had to do with a loose scope mount which allowed the scope to scoot backward minutely at each shot causing a vertical spread.
Check the rib on the No.1 too since it is screwed onto the barrel.