If you want to be a serious long-ranger, then just pick a bow - high skills make them the deadliest weapon in the field, and unlike NPC archers you can actually replenish your arrows when they inevitably run out. If you don't want to specialise in long range fighting, but want to be able to do it anyways, then take a crossbow - a little slower, but decent damage with perfect accuracy and high range.
Guns are just for close range defence and formation-versus-formation warfare.