I’m not gonna even try to explain why I’m wondering this. But I got to thinking, what if I want to shoot something underwater? I’d imagine that anything that uses gunpowder wouldn’t work, but AFAIK, most modern firearms wouldn’t have that problem. So how 'bout it, dopers? Is a .357 magnum useful against a shark? Or should I stick with a trusty speargun?
And for those who are interested in legal issues: no, I don’t want to shoot anyone. I’m just curious.
a quick google search turned this up.
http://www.hoboes.com/pub/Firearms/Technical%20Details/Underwater%20Firearms
Kind of an odd question, but…
Actually gunpowder wouldn’t necessarily be the limiting factor as most modern cartridges are fairly waterproof, although how long they stay that way would depend on how long they were submerged and how much water pressure they were exposed to.
The real limiting factor would be the weapon’s hammer style. An external hammer, which is common to most revolvers probably wouldn’t function due to water resistance on slowing the falling momentum of the hammer striking the primer. On the other hand, a weapon with an internal hammer where the firing pin is held under pressure by a mainspring would probably work fine.
As an aside, salt water is highly corrosive to both firearms and ammo, so unless you were interested in a one-time use I don’t think it would be worth testing.
Note that both weapons use darts.
The problem with firing underwater is not the propellant (I suspect that humans are sufficiently imaginative to protect even black powder from water long enough to fire).
The problem is that the round must wade through the water (much denser than air) which is constantly slowing it, and must first get rid of the (non-compressable) water in the barrel of the weapon to even begin its journey. I suspect that a barrel full of water is only slightly more dangerous to the shooter than a barrel half-filled with mud.
A weapon that fired the round without a barrel would only have to contend with the enormous drag of the water on the way to the target, but I doubt that it would be very accurate.
For a true “handgun” to be used reliably under water, I would think you’d need to continuously pump air into the barrel before firing. (Your range would still be extremely short. Anecdotal evidence suggests that a rifle or machine gun fired into the water loses its effectiveness within a couple of feet of the surface.)
Seriously Ultra my college dive coach demonstrated that with a plastic regular bucket and his Glok. He fired his 9mm into the bucket full of water and then picked the bullet right up out of the bottom of the bucket. we were at a BBQ at the coaches house before the season started he does it for all new recruits who think they will hit the bottom when jumping off the 40’ board…He does it to demonstrate basically exactly what ** tomndebb ** said. the drag has everything to do with it…I’d say a firearm discharged under water would have about the same efficacy as a port-a-potty in a hurricane 
Glock 17’s are designed to be fired underwater. Requires maritime spring cups to be installed in the firing pin assembly though.
One of many cites:
http://glock.missouri.edu/glock/glock1.shtml
Well, according to Half-Life, only the crossbow and the 9mm pistol function underwater 
Not sure that I want to rely on the gaming industry for accurate information on weapon designs. 
Thanks for the info, y’all.
It has nothing to do with oxygen for the gun powder or the drag on the firing mechanisms. If you try to fire any longarm (i.e. rifle) underwater the resistance from the barrel being full of water will cause the breech to explode, quite possibly killing you. And this is true for any powerful pistol as well.
Water is so dense it essentially turns the gun’s barrel into a pipe bomb.
All I know is what I see on TV, but there is a anti-shark weapon called a bangstick that uses shotgun shells. It houses the shell at the end of a rod (about 3 or 4 feet long, I think). If you need to kill a shark, you have to press the shell-end up against the fish and discharge it. Needless to say, this is for emergency use only.
MBA Gyrojet- This rocket gun projectile will go (still burning) underwater for a considerable distance (much further than a standard kinetic weapon) I have no idea about accuracy.
Our own Tranquilis has much more to say about the Gyrojet
Are there any advantages these “underwater” firearms have over a speargun underwater?
In addition to Hail Ants’ point above (if correct, I just don’t know enough about firearms to judge), wouldn’t it also be rather foolish to fire a firearm underwater?
Even if it would work, loud noises tend to be rather unpleasant underwater, and if you’re in close proximity to the weapon when you fire it, couldn’t you seriously damage your eardrums?
I have difficulty imagining any situation other than a military conflict where I would ever want to compound the risks of diving with use of firearms underwater.
Navy seals carry their weapons with then underwater and i imagine sometimes have to fire out the water with their weapon partialy submerged. So i guess it works.
That link takes you back to the front page, so I’ll paste the text.
APS Underwater Assault Rifle is intended for combat actions and self-defence from dangerous sea predators. It can be installed on special underwater vehicles and used against mini submarines. The rifle ensures delivery of aimed fire from any position of the swimmer including firing on the move. Additionally, the rifle can be successfully used for self-defence on the ground.
The rifle is loaded with MPS cartridge to hit underwater targets from the above-water position and vice versa.
At limit ranges in water the rifle ensures defeat of an enemy wearing a water suit with porolone padding and protected with a 5 mm thick organic glass.
The limit ranges of effective fire in water at different depths essentially exceed the visibility limits in most transparent waters of the world ocean.
Squirt gun.
SenorBeef’s link goes to the distributor (manufacturer?) of the weapon described in otto3883’s link. It is, effectively, a dart gun. (Note that in the specifications, the “bullet” is described as having a length of 120 mm (~6 inches).)
120 mm ~ 4 3/4 inches, not ~ 6 inches—still, a pretty long “bullet”
If it’s a one-time thing, how about putting a thin membrane across the end of the barrel? Something adequate to keep the water out, but which would offer no resistance to the bullet.
Is the rest of a gun sufficiently waterproof that no water would leak in that way?