My 581 series ranch rifle doesn't have holes drilled and tapped going down into the ring bases like some I have seen . I am posting a picture I grabbed off of YouTube with the tapped holes in the bases. Was this something Ruger did on a whim or is it serial number specific. I have seen these drilled and tapped this way on pre 581 guns and post 581 guns. Or have these been done after the fact by the owners.