Ammo questions...
It was always my understanding that using a handgun underwater necessitated usng fmj ammo due to the water having a stronger hydrstatic effect on expansion of hollowpoint rounds. Considering most people carry aggressive jhp's for deffensive carry, would those expansion forces be enough to expand the bullet before it left the barrel possibly damaging the firearm and potenially causing other damage? something to think about...

As an aside, glocks have an optional fluted firing pin cup for firing underwater. Most people don't have an 'operational' need for this.

Kuzushi,

Urban Myth all the way. I have shot or seen shot many different types of HP ammunition. When recovered, the bullet is undeformed. Firing into water is the most common way for forensics labs to recover tool marks on a round. The reason many use GI FMJ is that it is sealed both at the primer and at the case neck. Most commercial ammo is not. It may fail to fire after a few minutes to a few hours in the water.

The Glock amphibious firing pin is useful as it prevents the water from blocking firing pin motion. It does not always do it, but it can. More often when you get out of the water with a wet pistol. The flutes allow the water to drain quickly. That is the primary design concept of the pin, not for use underwater since the pistol becomes only a contact weapon below the surface.

Respectfully,

Jerry

It uses a spring loaded punch. Since my truck isn't an extended cab it would be hard to imagine the circumstance where I couldn't find anything to braced myself on.

Phaedrus,

From inside yes, but if you have to help someone else (as in this case) from the outside, it is a real problem. There is usually little or nothing to hang onto and nothing to brace against. In a public safety dive course we had several people try their EDC tools on a submerged car, none of them worked.

Respectfully,

Jerry

I could see that. It would depend on the type of vehicle, to be sure. My truck is old enough that it has door handles and mirrors mounted on tubular steel but many newer vehicles are much "slicker" on the outside. In a shallow river or other body of water that was waist deep or shallower you should get enough leverage from your legs but in a water over your head it would be an issue, for sure.