I just went through the AIM AI tutorial (it's pretty slick by the way). I had an unnecessary amount of trouble figuring out why you used the equation you did for Approximate aim until I realized that 500 was the bullet's speed. So I just thought maybe you should change the "500" to "Bullet[Bullet].Speed" in order to make the formula a little more transparent.
I made this change and uploaded the resulting cap here. While I was at it I changed the final layout title to "Perfect aim" from "Good aim" since that's what the heading says in that layout.