Andrew recently shot some handguns underwater and captured the results using a Pentax WG-2, a waterproof digital camera capable of taking basic high speed videos (which can be seen below). It’s interesting to see that the bullet does not travel very far underwater. The hollow point bullets also appear to blossom, almost turning inside out.
Andrew remarks that the pressure underwater from the blast feels like someone is punching you in you chest. He also said he fully inspected each handgun and did not detect any damage. Most important is that the sound/pressure underwater can be intense so sticking your head or ears underwater is obviously dangerous and not recommended.