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A Staff Report by the Straight Dope Science Advisory Board
Dear Straight Dope:
When a bullet is fired from land into water how
far can it travel? Movies portray a long trajectory, but I remember reading an
Ian Fleming book many years ago where he described that a bullet travels a yard
at most before it loses its speed and thereafter just slowly sinks. Given that
some bullets are more aerodynamic (hydrodynamic?) and some can have greater
speeds, how far can a bullet travel when fired into water? —A. A.
SDStaff Bricker responds:
It’s almost a shame that Cecil chose to assign this project to the SDSAB; it strikes me as a fine candidate for the sort of hands-on experimentation for which the Straight Dope is famous. However, you can see where letting Little Ed near live ammunition might not be entirely wise.
Besides, somebody beat us to it, namely the daredevils on "Mythbusters," who have a bigger budget anyway. In an episode airing July 13, 2005 on the Discovery Channel, the M-busters team built a water tank with thick acrylic sides braced with iron T-bars. Ballistics gel – in place of human flesh, thank goodness – was placed in the tank at various depths to simulate the terrified swimmer escaping a bloodthirsty assassin. The team collected a doomsday arsenal consisting of a 9mm semi-automatic pistol, an M1 Garand, a hunting rifle chambered for .223 ammunition, a shotgun, a .50 caliber "armor piercing" rifle, and, for fun, a replica Civil War-era black powder rifle.
In their first experiment, the experimenters shot the 9mm pistol straight down into the water. At a range of up to seven feet, the 9mm round was effective in completely penetrating the ballistics gel – meaning a person at the same range would be killed. At eight feet, the bullet entered but did not exit the gel, indicating a possible non-fatal wound. Past eight feet, the gel was undisturbed.
The shotgun, loaded with a 3” deer slug instead of buckshot, not only "killed" the ballistic gel target at six feet, it destroyed the acrylic water tank, ending that method of testing.
The team then switched to a swimming pool to continue the experiments – and to make the test more realistic, switched from shooting straight down to an angle of twenty to thirty degrees off the vertical, approximating a shooter standing on the edge of the water and shooting out into it.
The first candidate for this test was the Civil War rifle. At a range of 15 feet, the ballistics gel was completely unharmed; likewise at five feet. Only when the range was reduced to three feet did the bullet finally penetrate the gel, suggesting that diving under water was probably a pretty effective way of dodging slugs during the Civil War.
The experimenters moved on to the hunting rifle, which was loaded with a full-metal jacket .223 round that emerged at roughly 2,500 feet per second. At ten feet, the bullet disintegrated and the gel was untouched. At three feet, the bullet again broke up, with its tip coming to rest on the gel – not nearly enough power to damage flesh.
A bullet from the M1 Garand, with a muzzle speed of 2,800 ft/sec, also disintegrated at the ten-foot range. At two feet, the slug penetrated about four inches into the gel, suggesting a non-fatal wound. The armor-piercing .50 caliber round didn’t do any better – it, too, came apart at distances greater than five feet and lost most of its punch by three feet.
The Mythbusters team concluded that you’d be safe from firearms even if they were fired straight down to a depth of eight feet, and probably safe at much lesser depths, especially if the bullet was aimed at an angle.
But that’s not the whole story, although it's the most dramatic part. In our ingenious age, for almost any imaginable environment, chances are there's somebody who's figured out a way to shoot guns in it. It's even so with shooting into (or under) water.
The problem that the Mythbusters faced was mostly due to the shape of the
bullets – what works well in air isn't an advantage underwater. Rifling of a
barrel, which cause the bullet to spin and provides aerodynamic
stability, is useless in a water environment.
The engineers at the Central Scientific Research Institute for Precision Machinery Construction in Moscow correctly perceived the problem with shooting into water and in response developed the SPP-1 (Spetsialnyj Podvodnyj Pistolet, or “Special Underwater Pistol”) for use by Russian Navy frogmen. The SPP-1 is a manually operated four-barrel handgun that breaks open along the top and loads in a fashion similar to a double-barrel or over-and-under shotgun. The ammunition is designed to work underwater, using long bottlenecked rimmed casings plus bullets made from mild rather than hardened steel and designed to be stable underwater. The barrel isn't rifled. According to the specs for the pistol, when fired at a depth of five meters – over sixteen feet – it's lethal up to seventeen meters, or over fifty-five feet.
The SPP-1 isn't the only exemplar of the breed. Other firearms are designed to work underwater as well, but they tend more towards the spear-gun model using dart-like projectiles. There’s no bright-line boundary where a bullet becomes a dart, but the projectiles fired by the Heckler & Koch P11 Underwater Pistol, for example, clearly cross the line. The H&K is an all-polymer weapon made especially for underwater use by the German Bundeswehr Kampfschwimmer – “army combat divers.” Each of the five dart-shaped projectiles is powered by a small, solid-fuel rocket. The weapon has been featured in some high-profile films, including Tomb Raider with Angelina Jolie, and is said to be able to inflict a fatal wound at fifty feet underwater.
So the general rule is that most ordinary guns and bullets aren't tremendously effective when fired into the water, and if you can dive below eight feet, you’re probably safe from your run-of-the mill assassins. But if you’ve incurred the wrath of the Bundeswehr, all bets are off. You may as well stay dry and meet your fate like a man.
Straight Dope Science Advisory Board
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Staff Reports are researched and written by members of the Straight Dope Science Advisory Board, Cecil's online auxiliary. Although the SDSAB does its best, these articles are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.
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