Thread: How well do bullets swim?

Picture a scene you've seen in a thousand action films.

Our intrepid hero drives off the dock into the bay to escape the heavily-armed evil hoodlums in hot pursuit. Seconds later, said heavily-armed hoodlums are rapid-firing towards the submerged vehicle as our hero struggles free. Rifle rounds are penetrating to the ~5m depth of the wrecked vehicle sitting on the bottom. Peuw peuw go the bullets, leaving little bubble trails all around making it crystal clear that our intrepid hero is in real danger ...

... except, yes, they are ~5m under water.

So do bullets fly, at speed, under water? I think not.

Using my Ninja googling skills, sure enough it turns out a gun fired under water horizontally at a brave scientist/foolhardy Darwin award candidate flies for maybe a metre or two in a parabolic arc to the floor.

Question is, is that simply physics due to the density and viscosity of water, or a side-effect of firing the gun under water rather than from the dock side down into the bay?