So he can fire a Glock modified for firing underwater, underwater. I'm sooooo impressed. :roll:
Here's what glock says about pistols firing underwater. I especially love the first line, and the line about the meritime cups this guy in the video is using.
http://glockfaq.com/generalinfo.htm#h2o
"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."
"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."