For 40 years and still going the standard Redfield type base w/the rear windage adjustment screws have been mounted on a 270 Win.
Move up to 338 RUM. Same mounts. Maybe 100 shots and the rinky dink windage screws came apart. Can't recall for sure but I think the little "tab" on the ring base let go.
Immediately installed a 'key'd' (can't recall the proper terminology) rear base an bought a set of rings to go with. Seems good so far.
Next is my 270 AM. Accuracy/repeatability went to pot. 800 rounds. Same 'trusty' Redfield/Leuy one piece base w/windage screws. Took the rifle apart. All screws tight except one windage screw. Tightened it and consistency greatly improved but not to where it was.
Further inspection shows a distinct silver ring cut into the scope base 'tab'.
I think that the screw is actuall tightening against the base and leaving a few/part thou of rear scope movement.
Now......What's the story on that base in the pic...........?
One can only hope that 'all' 700s/721s are drilled the same.