1999


From: New Scientist

How to vary the speed of a bullet so it won't kill your target

A TWIST of a dial on a gun can turn a deadly bullet into a non-lethal projectile and back again, thanks to a new propellant developed by scientists at the Oak Ridge National Laboratory in Tennessee. The invention may allow police to control rowdy demonstrators with rubber bullets fired at a slower speed so that they don't kill.

"Though rubber bullets are intended to be less than lethal, at short range, they can be fatal," says Carl Pocratsky, the project manager for variable-speed bullets with the Department of Energy. "But if you can adjust the velocity, you can avoid that."

Rusi Taleyarkhan and his team at Oak Ridge have invented an aluminium-based propellant. When aluminium reacts with water at high temperatures, the aluminium oxidises releasing energy and hydrogen in the process. This reaction releases four times as much energy as burning gunpowder. The key to varying the speed of the bullet lies in the light weight of the propellant, making it suitable for handguns. However, the reaction is difficult to get started, says Taleyarkhan. "The aluminium forms a protective oxide layer, and it's tough to get rid of the barrier." Taleyarkhan has managed to destabilise the oxide with an additive so the reaction can start. He refuses to say what the additive is, because patents are pending.

Because a charge made out of aluminium slurry is so light, Taleyarkhan has been able to put four separate charges into a shotgun cartridge. By controlling how many of the charges in the cartridge fire and at what time, Taleyarkhan's team can manipulate a projectile's speed. They can even accelerate a bullet so gently that it can be made out of very fragile materials. "We've shot little fluid slugs, bath balls with perfume, paint balls, jello slugs-everything I come across, I use," says Taleyarkhan. Pocratsky says it should be possible to link a rangefinder to the control mechanism, so that rubber bullets will automatically be fired with a reduced charge at close range.

Author: Charles Seife, Washington DC New Scientist issue 12 June 1999

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