Complex sentence: The first is to shoot only when the rifleman considers the wind to be the same as with previous shots, the second is to purposefully change the point of aim, just as one would do with a conventional rifle.
Split into simpler sentences: The first is for the rifleman to shoot only when he considers the wind to be the same as with previous shots. The second is to purposefully change the point of aim, just as one would do with a conventional rifle.