Found this online.
confirmed
Bullets Fired Into Water
Original Bulletproof Water episode
This time around, they want to test if it was possible to fire ordinary guns underwater. There were to questions in particular they wanted to answer:
* Will an regular gun fire underwater?
* At what distance is would a bullet (from a regular gun) fired underwater be lethal?
Test setup:
* Water trough that the bullets were fired through
* Movable ballistics gel target to test lethality
Test weapons:
* Colt King Cobra, .357 magnum full metal jacket
* Sig Sauer P239, 9mm
* M1 Garand/.30-06
* 12-gauge shotgun
There are Special Forces guns that can fire underwater (Glock 17, Russian SPP-1 underwater pistol), but they wanted to test whether 'regular' weapons could do the trick.
Tory made sure that there was no air in the barrel because, if there was, the barrel could explode.
The first up was the 9mm. Without a ballistics gel target, the bullet went 18 ft. This answered the first question: yes, you can fire a regular gun underwater (confirmed). The 9mm bullet was intact, but the casing wasn't ejected from the gun. Instead, it was stuck in the slide, so you would only get one shot underwater.
Now they had verified that you can fire a gun underwater, they moved onto testing lethality. In the original episode, they found that a 9mm gun fired into water was lethal at 8ft. No so for a bullet fired underwater: the 9mm bullet didn't even come close to penetrating the target at 10ft. They next moved the target to 2ft, at which point they couldn't find the bullet. Same with the .357 magnum: they lost the bullet when fired at 2ft from the target.
Back at the shop they dissected the ballistics gel block and found the 9mm at 4" deep and the .357 magnum at 5.5", i.e. both would be lethal at 2ft.
The other guns didn't fare as well. The 12-gauge shotgun cracked on firing with heavy damage to the barrel and stock. The impressive M1 Garand also fared poorly. The M1 has an exit velocity of 2700 ft/s, 3 times the energy of the other guns they were testing, but in the original Bulletproof Water episode, they had already seen it fail to shoot into water -- bullet shattered on impact. The firing underwater was equally unimpressive: the bullet was intact, but it only went 6 ft, less distance that the 9mm.
You can fire a bullet from a rifle or handgun underwater: confirmed (you can't use a shotgun underwater). However, it is more lethal to fire into water than it is to fire underwater.