Railgun

A railgun uses the Lorentz force to fire a conductive projectile at high velocity. The projectile slides down two conductive rails, connected to a high current power supply. When a massive electrical current passes through the projectile, the Lorentz force pushes the projectile in a direction perpendicular to the current flow. By using an electromagnet above and below the rails to set up a vertical megnetic field, the Lorentz force can be constrained to a direction parallel to the rails.

A railgun consists of two parallel rails, one conducting piece of ammunition, and some power source, like a capacitor. The rails are attached to some non-conducting base, with the ammunition (often a copper slug) placed between them such that it touched both. A wire (or metal rod, depending on the current you want) is attached to each rod, and when you are ready to fire, you touch the leads of the cap to the two wires (rods).

The railgun works by the force that is created when a current runs perpindicular to a magnetic field. The current in this case is between the rails, through the copper slug. The magnetic field is created by the current through the rails. The force is dependent upon the energy stored in the cap, so large caps and caps in parallel are a good idea here. The slug will attain extremely high velocities with this railgun, and it is possible to shoot paper clips through bricks with big enough caps.

I recently watched a special about these kinds of weapons on the Discovery Channel and there are a few clarifications I'd like to make.

First of all, the slugs that are fired are usually made of a heavy metal, like Tungsten.  Sometimes, depleted Uranium is used (think of where else it's used-- the A-10's GAU-8A Gatling Gun).  Also, a metal casing is used around the slug, so that once it clears the rails, the drag in the air splits the casing off, revealing the smooth slug.  From what they said, the slug can travel at speeds in excess of 10 times the speed of sound. 

Railguns as weapons could well see use in space-based platforms, since the airless environment would dramatically improve their efficiency. Such craft would mostly be used for destroying enemy sattelites, I would imagine.

The pressure difference of the gas-injection system would be maximised by the pressure gradient with a vacuum rather than atmospheric pressure, the resultant increase in muzzle velocity would be useful if not vast.

But more importantly, you don't ionise air and fuse the rails when there's no air to ionise, so the railgun, along with being supercooled, can operate far longer and over many more shots without maintenance.

They even become, technically, semi-automatic when used in such circumstances.

NASA is already considering railgun technology as an alternative method of launching supplies into space, although at the moment costs remain prohibitively high.

The railgun has become a firm favourite weapon of players of the Quake series of first-person shooters, despite only having been part of it since Quake II. It is the series' nearest equivilant to a sniper rifle, and it is considered the mark of a true professional when one can pick off opponents with only a single, well-placed shot. It has so far appeared in Quake II and its mission packs, and Quake 3 Arena (with its expansion, Team Arena).

The weapon uses depleted uranium slugs as ammunition, firing them at colossal speeds until they hit concrete. In Quake II's single player, it was easily possible to fire through several weaker enemies with a single shot, gibbing all in its path; stronger enemies would typically take numerous shots to bring down. The weapon truly came into its own in deathmatch, however, where its unlimited range made it a truly dangerous weapon in the hands of a master. (The caveat, of course, was that it soon become known as a camper's weapon.)

Quake 3 Arena, being entirely multiplayer-orientated, toned down the weapon considerably: damage was lowered, and the already lengthy reload time was also increased. It still remains a powerful weapon, however, with one-shot kills being possible upon unarmoured opponents. Team Arena went even further, lowering the damage so much that the weapon's usefulness became quite questionable.

The Quake 3 version of the weapon also did away with the classic (some would say beautiful) corkscrew-particle effect that appeared when the weapon was fired in Quake 2. This was done to avoid horrendous drops in framerate when rendering the particles in the new engine. However, the effect can be reproduced by entering the following command at the console:

/cg_oldrail 1

The rail gun is a type of projectile weapon that uses a propulsion system different than the common gunpowder devices.

The rail gun is thus named because of the twin rails that make its usage possible. There are four basic components of a rail gun. The power supply, the rails, the armature, and of course the projectile. The power supply sends a current down one rail which comes back through the other rail by going across the armature. The armature is a conductive bridge that is allowed to move freely on the rails and which also holds the projectile. Whenever a current travels over a wire, a magnetic field is generated. Each rail acts as an individual wire and each generates a force that spirals around it. The forces of the two rails form a vertical upward force between them.

Meanwhile, the armature and projectile experience a Lorentz force. This force runs perpendicular to both the magnetic field which runs vertically and the current which runs horizontally. The only other way to move is parallel to the rails. The projectile-carrying armature is pushed with the Lorentz force according to the equation F=i*L*B where F is the force, i is the current, L is the length of the rails, and B is the magnetic field.

Building extremely long rails can pose design challenges. Therefore, most rail guns use extremely high currents, usually up around one million amperes while the rails are usually around four to nine meters in length.

The most outstanding advantage the rail gun has over gunpowder weapons is its sheer power. A gunpowder weapon can only fire with a velocity around 4,000 fps. The rail gun smashes this record with velocities around 52,400 fps. The United States Navy rail guns currently have an accurate maximum range of around 12 miles. Rail guns can reach a target 250 miles away in approximately six minutes.

Other advantages are that gunpowder ammunition is volatile and requires more caution than rail gun ammo. Gunpowder ammunition includes the casing, powder, and bullet, making the round heavier than a similarly sized rail gun round.

Along with advantages naturally come obstacles. Some of the obstacles facing the rail gun are:

• Power supply-Rail guns require very high amounts of power to operate. The capacitors used to store the necessary charges are several cubic meters in size.
• Heating-Wherever there is resistance, there is heat. With the amount of current running through the rails, lots of heat is generated even though rails are made of very conductive materials. This along with the friction generated by the swift moving armature can damage rails.
• Repulsion-Because one rail is the positive rail and the other is the negative rail, the rails repel each other very strongly when a current is sent through them. For this reason, rails usually do not last for more than a few firings before they must be replaced.

So until we find a way to generate massive amounts of electricity all at once, rail guns have yet to find common usage on the battlefield.

My railgun is hard and ready for fun,
the barrel is hot and long and the capacitors are done.
Whining and moaning and straining at the rails,
we undress before the shrouding as modesty fails.

A touch on the trigger, a shuddering, tantalizing moan,
hard and hot and accurate, magnetic poles will groan,
Lorentz is kind and willing the projectile always comes,
as I do, my lasers primed and ready in my superheated guns.