The force or resistance that a fluid offers against the movement of an object moving through it, is called drag. Underwater a bullet has to work extra hard against the water’s natural drag (resistence, just like when you swim in water) to continue moving forward. Most bullets, they do not go beyond a few meters. If you shoot the bullet above the water into the water, this drag is increased, as the bullet ‘pancakes’ against the water surface, unless it is a special cavity bullet. Imagine the force of your body against water if you dive versus if you belly flop? The bullet can often hit the water more like a belly flop or a bad dive, and therefore has to work extra hard against the drag of the water to move forward.