RAILGUN- A 21st century weapon

The fine gray powder does have three major limitations:

• Gunpowder must be carried with the projectile, making the entire round heavier.
• Ordnance based on black powder is volatile, and so difficult to handle and transport.
• The muzzle velocity of projectiles propelled by gunpowder is generally limited to about 4,000 feet (about 1,219 meters) per second.

 One solution to overcome these challenges is the electromagnetic rail gun, or rail gun for short. Using a magnetic field powered by electricity, a rail gun can accelerate a projectile up to 52,493 feet (16,000 meters) per second. And while current Navy guns have a maximum range of 12 miles, rail guns can hit a target 250 miles away in six minutes.

A rail gun is basically a large electric circuit, made up of three parts: a power source, a pair of parallel rails and a moving armature.

1. The power supply is simply a source of electric current. Typically, the current used in medium- to large-caliber rail guns is in the millions of amps. 
2. The rails are lengths of conductive metal, such as copper. They can range from four to 30 feet (9 meters) long. 
3. The armature bridges the gap between the rails. It can be a solid piece of conductive metal or a conductive sabot -- a carrier that houses a dart or other projectile. 

Some rail guns use a plasma armature. In this set-up a thin metal foil is placed on the back of a non-conducting projectile. When power flows through this foil it vaporizes and becomes a plasma, which carries the current.

Here's how the pieces work together:

An electric current runs from the positive terminal of the power supply, up the positive rail, across the armature, and down the negative rail back to the power supply.Current flowing in any wire creates a magnetic field around it a region where a magnetic force is felt. This force has both a magnitude and a direction. In a rail gun, the two rails act like wires, with a magnetic field circulating around each rail. The force lines of the magnetic field run in a counterclockwise circle around the positive rail and in a clockwise circle around the negative rail. The net magnetic field between the rails is directed vertically.

Like a charged wire in an electric field, the projectile experiences a force known as the Lorentz force (after the Dutch physicist Hendrik A. Lorentz). The Lorentz force is directed perpendicularly to the magnetic field and to the direction of the current flowing across the armature.

The magnitude of the force is determined by the equation F = (i)(L)(B), where F is the net force, i is the current, L is the length of the rails and B is the magnetic field. The force can be boosted by increasing either the length of the rails or the amount of current.The projectile, under the influence of the Lorentz force, accelerates to the end of the rails opposite the power supply and exits through an aperture. The circuit is broken, which ends the flow of current.

Rail guns are of particular interest to the military, as an alternative to current large artillery. Rail gun ammunition, in the form of small tungsten missiles, would be relatively light, easy to transport and easy to handle. And because of their high velocities, rail gun missiles would be less susceptible to bullet drop and wind shift than current artillery shells. Course correction would be important, but all missiles fired from rail gun artillery would be guided by satellite.