Mythbusters, guns, and H2O

[strredwolf]

Today's Mythbusters tested a myth in which if you're under water, you can be protected from firing bullets.  While unconfirmed for 9mm (10+ feet, we really need to firmly test this), shooting 233's, M-1's, and 50mm into water is confirmed at over 5 linear feet -- they distentigrate when they hit the water over a distance over three linear feet.

Linear feet, aka distance from the target to the gun.  Not how deep you're in.

Why did they disentigrate?  Well, you're shooting bigger bullets faster, which will have more resistance when they hit the water (which is roughtly still).  Equal and opposite force pushing back, which means they could be hitting the theoretical slice of lemon wrapped around a gold brick, which was piled up against a thick wall of steel and concrete.  The 9mm, the bullets are fast but they're light enough so that they can't disentigrate, they just go straight in.

I really want to see what distance of water that 9mm needs to traverse before water friction gets the better of it.

Comments

[griffinwolf.livejournal.com]

No, it has to do with the surface tension of the water. At higher velocities, especially the 'supersonic' rounds they're using for the 50-cal, etc, means that the impact time at the surface of the water greatly reduces. It's this impact on the surface of the water which renders these rounds completely useless, because there's a much greater force.

For the 9 mm rounds, the impact time is much greater, which means the water has time for the surface to be broken, and the round to proceed through.

The mass of the round is farely negligable. What I would REALLY like to do is see the type of surface tension water has, compared to the drag forces the bullet faces under the surface of the water. I'm not sure how they'd measure the surface tension, but I'm sure that, for an underwater environment, a Reynolds number would be used ;)

[rhanlav.livejournal.com]

One of the best Mythbusters episodes ever! I rate it just below them blowing up the concrete truck for no good reason. ^_^