For decades, it has been theorized that polymer-framed handguns can be safely fired underwater with normal loads. For every mention of this, a dozen warning signs and flags soon follow that advocate it is simply an urban legend that will wind up injuring the user. Well, about that...
Can it be done?
The short answer to this question is: Yes*. The asterisk is in the all-important details of this. While the Hi Point itself was not specifically designed from the ground-up to be an underwater frogman firearm (unlike the Soviet SPP-1 or the HKP11) and such vaunted polymer-framed gatts such as the Austrian-made Glock can be modified to do so with special internal parts and ammunition, its not impossible
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.
Glock solves this with special firing pin bushing cups that allow water to drain from submerged guns but even with these cups 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 Hi Point Balloon Gun
Back in August 2013, a team from HP conducted tests on a standard C9 9mm Hi Point pistol with the handgun fully submerged.
In a post on their Facebook page they joked that, "Yes it is the new hi-point underwater 'balloon' gun! We don't advocate shooting any firearm under water all of these tests were done at our private river "X" testing facility No fish were hurt during these tests!"
According to Hi Point, "The round only goes about 3 feet out. We picked up the bullets we could find. The C9 wanted to load the next round but the empty wouldn't get out of the way."
So, yes, Virginia, it can be done, but should it? Well, we think you already know that answer...
The company has also put out its own torture test video highlighting the use of a 995 series carbine when thrown in the water (however they don't fire it while submerged and don't advocate that you do so either)
Sorry guys, try to keep your Hi Point above water, or keep your accidental death and dismemberment insurance up to date.