Assume we are shooting a rifle that is already correctly sighted in. When we put the rifle to our shoulder and line up the sights on the target, we are looking along the line of sight. This line is perfectly straight, as only light can be, and runs from our eye through the rear sight, then the front sight, then to the spot on the target we want to hit. Unfortunately, this doesn't coincide with the flight of the bullet or ball. Since the bore of the rifle is below the sights, the bullet starts out below the line of sight, crosses it traveling upward, stays above it for a time, then begins to fall downward, crossing the line of sight exactly at the target. Every shot we fire will travel this curving loop.
*The bullet will reach its maximum height above the line of sight at about 60% of the distance to the target, and this point is called the Mid-Range Trajectory. Once the bullet travels past the target, it will be below the line of sight until it stops, for whatever reason.
