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.
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