Looking for a no frills, freehand, minimum prep solution to the challenge with a totally bog-standard set-up; I decided to use the zoom on the scope to fix my zero at the intersection of the vertical cross-hair post with the scope's bottom margin... unfortunately this resulted in a mag of only x4 or so to shoot with.
Now I usually prefer a malt whisky but at 206 yards and x4 that bright white tin stood out a treat against the red paint on the old barn...