There has always been an urban legend passed around internet message boards and wherever Glock enthusiasts meet-- that of the gun being designed to fire underwater. Here at Glock Forums we decided to go for the truth on this.
Can it be done?
The short answer to this question is: Yes*. The asterisk is in the all-important details of this. While the Glock itself was not specifically designed from the ground-up to be an underwater firearms (unlike the Soviet SPP-1 or the HKP11 ) it can be modified to do so with special internal parts and ammunition.
(photo by Vuurwapen)
The Specifics of the problem
When a firearm is completely filled with water, the explosion of a self-contained cartridge being fired in the chamber of said firearm needs some place to go. This pressure wave can destroy the gun itself. This is because the gun was designed to fire in normal atmosphere where gravity and the nitrogen/oxygen mix of surrounding air have predictable effects. If you remove the easy to displace air and switch it out with a solid wall of water, you have a dangerous situation. Ever seen one of those old WWII movies with a depth charge going off over a submarine? The depth charge isn't made to blow the submarine up, but rather to force a wave of water to crush the sub.
It's the same concept.
To solve the problem of making the Glock amphibious, the company has long made a series of special firing pin bushing spring cups (item number #8 on the parts diagram).
These cups have four channels along the side to channel water away when the gun in fired underwater. It solves the problem of light spring strikes and gives the gun the capability to fire more often than not underwater.
Even then, the gun is extremely dangerous to the user (if submerged) in so much that, the water around it, due to the sudden overpressure, can be forced into the ear canal of the user due with possibly bad consequences. As such, the company limits sales of these items to military and LE units and most training is done in shallow water or swimming pools with the user's head (and thus eardrums) safely above water. The Glock 17 using NATO specification ball (not +P) ammunition will completely penetrate a minimum of one 1/2" pine board at a distance of ten feet from the muzzle when fired underwater.
However they are sold in aftermarket by Glockmeister, Lone Wolf and on Amazon (by GHOST) for anywhere from $8-$20. Of course, everyone of these sellers will not be held responsible for damages incurred when using said product.
A Great video by Twang and Bang on the use of Maritime Spring Cups
Should it be done?
Yes, you may have seen the great work by Mythbusters and the wonderful images on Vuurwapen of firing a gun underwater. It can be done but it is still extremely dangerous. The use of a Glock 17/19 with the so-called 'maritime' or 'amphibious' cups makes it marginally safer, but it's still not advisable. Those very small groups of underwater special operations types that use these guns with an elaborately mandatory series of safety protocols that includes hearing and eye protection-- and even then, it is rare.
Sorry guys, try to keep your Glocks above water, or keep your accidental death and dismemberment insurance up to date.
Or just leave it to the Steve Zousso crowd