Was down at the PD match on Saturday and got to thinking about this, so I did the math.

BD = Bullet Drop
A = Angle rifle is canted from vertical
E = error, left or right

E = BD tan A

Example:
At 425 yards, my .308 drops 31" with a 100 yard zero. If my rifle is canted 5° from vertical, the windage error is:

E = 31" X tan 5°

E = 31" X 0.0875

E = 2.71"

Here's another example because 5° is a lot and 425 yards isn't.

Same rifle at 1,000 yards, bullet drop is 321". Assume cant of only 2°, which seems more realistic.

E = 321 tan 2°

E = 11.2"