Is it possible to fire a Glock 17 underwater?

If you have one in the chamber it will fire. Not sure if the water resistance will keep the action from cycling, or not, you may or may not be able to fire another round, etc. The water will also have a serious detrimental effect on velocity. Target should be within a couple of feet, I'd guess, for any kind of effectiveness. Sound will probably be magnified as water is more efficient in carrying sound waves - better have your ear protection on!