What is the change at 20 and 30 yards? If there is non then I would adjust the 40 yard pin to the point of impact.
If the 20 and 30 yard shots are also drifting then check the rest for centershot as it sounds like the rest is too far left causing the center of the arrow shaft to be pointing and shooting to the left.
I had this problem when I first got my recurve as I ordered it to be centercut so I could use my compound arrows and a duplicate rest. It wasn't and the rest caused the same type of drifting as you are experiencing.


Greg

"Getting close to the game is the joy of Bowhunting for me, the harvest is a bonus."

Live 15 ft Python after eating a small Antelope!