Just about any handgun will fire underwater -- at least once. :-) However, firing underwater is NOT recommended because it can have devastating effects on the pistol and the shooter -- a potentially dangerous activity that should only be utilized by trained personnel wearing proper equipment for protection against potential pressure wave effects of underwater detonation. The shock/pressure waves in water can really damage internal organs (ever heard of lithotripsy?). Shooting a pistol underwater can lead to property damage, serious bodily injury or even death.
NOTE: Glock, Inc., specifically disclaims any and all liability from anyone performing or attempting to perform underwater firing with a Glock pistol -- you do so at your own risk.
The Glock 17 may be equipped with an optional set of maritime spring cups for use in water environments. Maritime spring cups are not intended for submerged firing, but for surface use by special ops teams who operate in and around water. The maritime spring cups are two small parts within the firing pin assembly and are not included on any Model 17 sold by Glock (civilians can only get them through 3rd parties). They insure that water can pass by the firing pin within the firing pin channel, thus preventing the creation of hydraulic force within the firing pin channel -- which would slow the firing pin down, causing light primer strikes. With the special cups, the action will cycle reliably while submersed, if a little bit slower. NATO specification ammunition (such as Winchester's Ranger RA9124N) with waterproof sealed primers and case mouths is recommended.
Although you may install the maritime spring cups on any Glock model, *only* the Glock 17 was designed and intended to use the modified spring cups for aquatic firing -- and only then using 9mm ball ammunition to remain within acceptable pressure limits. The foolhardy who insist on living dangerously must keep several things in mind: The Glock 17 must be fully submersed underwater. There must not be any air left within the pistol as the muzzle is pointed towards the surface of the water after submersion to allow the air in the barrel to escape. Use only full metal jacket, ball-type ammunition because the water within the barrel can spread a hollow point out within the barrel upon firing. This increases the bearing surface of the bullet to the barrel and could catastrophically increase pressures. Even if the barrel doesn't burst, the expanded bullet would get even bigger upon exiting into the water and would slow down very quickly while tumbling. Accuracy would be terrible.
The marinized Glock 17 is primarily for use by various Special Warfare units operating in aquatic environments. At least one specialized Scuba diving group regularly uses G17's to dispatch sharks where they dive. The Glock 17 using NATO specification ball ammunition will completely penetrate a minimum of one 1/2" pine board at a distance of ten feet from the muzzle when fired underwater.
Trained personnel who use Glocks underwater know they must obey several rules:
1) use only a Glock Model 17 with amphibious spring cups (reliability issue);
2) use only 9mm FMJ subsonic, sealed primer ammo;
3) completely immerse the pistol and get *all* the air out of the barrel;
4) wear protective ear plugs, gloves, wet suit, face mask, etc.;
5) do not fire near solid objects or in enclosed spaces to prevent return
However, any Glock -- even those not equipped with maritime spring cups -- will normally fire while submersed underwater. But doing so may generate excessive internal pressure and may cause the pistol to literally blow up. This is especially true with the use of high-pressure rounds (such as the .40 S&W/357 SIG) or hollow-point bullets.
I recall a reported incident where a Glockster on a boating holiday decided to show some friends how his Glock would fire underwater (because Tommy Lee Jones said so in the movies). He stuck his hand overboard, pulled the trigger and came back with a bunch of shredded plastic and a badly injured hand.
Another reported case was the Glockster who decided to try out his Glock 23 .40 S&W in the swimming pool after seeing pictures of Glocks being fired underwater on the web. He was totally submerged, with the gun, as he fired at a piece of wood on the bottom of his pool. The Glock did fire, the .40 S&W FMJ round left the barrel and went into the wood. The chamber also exploded and implanted shrapnel into his leg. Thinking that the water would muffle the blast, he did not wear hearing protection (the blast is actually about 4 times louder underwater). He is now mostly deaf in one ear and hears high-pitched tones most of his waking life.
As you can see, firing a pistol underwater is a *very* dangerous endeavor.
Several things could happen:
1) the firing pin may be slowed enough to not detonate the primer
(without the maritime spring cups)
2) the pistol could blow up in your hand;
3) the concussion could damage ears, eyes or internal organs;
4) the bullet may not go where you intend it to.
Even if you have the right equipment, know what you're doing and follow the rules -- the risks for underwater firing are minimized -- but not eliminated. Your pistol's barrel could be affected by water obstruction and your body by damaging concussion. By using hollow point bullets (water may cause the bullet to expand in the barrel), high pressure ammo, etc. -- you're asking for an underwater kaBoom! It you fire near solid or hard objects, the bouncing concussion can cause extensive, perhaps even fatal external/internal tissue injury. Why risk it? [JT]
Here are some pics from [G29 Man] shooting his G26 underwater.