long distance accuracy
As you shoot at longer distance, variables enter the equation that most of us never have contended with. For example, the Coriolis effect which for North America is a deviation to the right caused by the earth rotation. To make matters worse, rifling rotates to the right so the bullet starts moving to the right. So 2 separate effects cause a right movement deviation. At 100 yards, these effects are relatively insignificant. At 1000 yards they are significnt and at 2000 yards they are almost ridiculous. Other factors include atmospheric pressure, temperature, wind and others. Moral here -- at extreme distances everything becomes an issue.