Stun gun vs. Coilgun vs. Gauss Rifle vs. Railgun vs. EMP Weapon vs. Tesla Cannon

There is a lot of confusion over weapons that use electricity rather than explosives, fuels, or compressed air to deliver damaging energy to a target. Many sources, most commonly video games and roleplaying games, will call a Gauss rifle a railgun, or confuse a coilgun with a Gauss rifle, or worse, assume these terms are interchangeable. In fact these weapons rely on very different principles.

The railgun is the most difficult to understand, and the coilgun and Gauss rifle are easy to confuse since they both use magnetic force to launch a (usually) iron projectile. Additionally, the stun gun, Tesla cannon, and EMP bomb all use electricity to damage targets, in these cases using electricity directly rather than imparting kinetic energy to a projectile.

The stun gun and the coilgun are both relatively practical devices, although the coilgun is currently more of a hobbyist's toy than a weapon. The Gauss rifle and EMP bomb are both theoretical, but there is no reason they couldn't exist. Real railguns have been built by both the US military and hobbyists, although firing the projectile causes extreme wear and abrasion on the rails and so has thus far proven impractical as a weapon because the rails must be serviced between shots. The Tesla cannon is pure fiction, however, as there is no theoretical way to aim such a device.

Although many of these devices are relatively silent in that there is no explosive propellant, any projectile traveling faster than the speed of sound in an atmosphere will create a sonic boom. With small bullets, this is merely a distinctive "crack". Larger artillery shells, such as the ones the US military has been using to experiment with rail guns, would make a very loud sonic boom. Lack of an explosive propellant (and in most cases also muzzle flash), however, reduces the chances of an enemy discovering your firing position.

Listed from most realistic to least:

Stun gun

Technology
A stun gun or taser uses a high voltage, low current electrical shock to incapacitate a person without causing any serious or long-term damage. Since any animal's muscle control is a result of electrical signals traveling up and down nerve pathways, a strong electrical jolt can cause a variety of effects, such as pain, involuntary muscle contraction, or even convulsions. Tetanizing tasers use a series of short duration, high voltage pulses to confuse the muscles, causing temporary paralysis. There are two basic types, short-range (stun gun) and long-range (taser).

Short range stun guns consist of two electrodes that must be pressed to the victim's body to deliver the shock. Long range tasers contain two needles which, when fired, trail a wire behind each of them leading back to the taser. The needles embed themselves in the victim's body and the shocks are administered though the wires.

Stun guns are relatively safe because they are current limited. That is, although they generate very high voltages, they are incapable of generating high currents, which is what does most of the damage to flesh and internal organs in an ordinary electric shock. Stun guns are very similar in principle to a cattle prod.

Applications
Law enforcement, crowd control, non-lethal self-defense, torture.

Limitations
There is some controversy over whether stun guns give people a false sense of security, as an aggressor could potentially take the device away from and use it on the victim. Short-range stun guns require you to be in grappling range, and long-range tasers are one-shot weapons. Although several jolts can be administered by the launched electrodes, you have problems if you miss or there is more than one opponent. Additionally, they do not work through heavy clothing such as leather jackets.

Coilgun

Technology
A coilgun uses one or more solenoids, or coils of wire, wrapped around the barrel. When electric current is applied, a magnetic field is created in the coil which pulls a ferrous or magnetic projectile down the barrel. Multiple coils can be used in succession to increase the projectile's velocity. Except for a possible sonic boom from the bullet, a coilgun is completely silent.

Building coilguns is relatively easy compared to the other types listed here, and is a popular amateur project. Battery powered hobby coilguns use a bank of capacitors and a voltage pump circuit to convert low voltage battery power into high voltage pulse for use in the coil. Because of the limitations of the battery output, it can take a minute or more to charge the capacitors between shots.

Applications
Silent firearm, launching vehicles or cargo into orbit from the Earth or the Moon, launching material mined from asteroids into Earth's orbit for pickup.

Limitations
The coilgun, although the easiest to make of the list, is also the weakest. The solenoids are not as strong as a string of electromagnets found in a Gauss rifle and the forces are far weaker than the Lorentz force generated by a railgun.

Gauss Rifle

Technology
A Gauss rifle uses electromagnets down the length of the barrel. A simple version would use two electromagnets at the end of the barrel to pull a ferrous or magnetic projectile forward between them. These electromagnets must be turned off just before the projectile passes them, or a force will be applied backwards, slowing the projectile. A succession of electromagnets can be used down the length of the barrel to increase the velocity of the projectile. Like the coilgun, a Gauss rifle is completely silent.

Applications
Similar to the coilgun.

Limitations
A Gauss rifle requires absolute precision timing to get the most out of the electromagnets, which can be very difficult given the speeds required to make it an effective weapon. Turning them off too soon will reduce the time they are able to generate force on the projectile, and turning them off too late will cause them to pull backward on the projectile after it has passed the magnet.

Railgun

Technology
A railgun uses two electrically conductive rails and a conductive projectile. This is not a standard magnetic projectile weapon. Although magnetic fields are generated, the projectile will fire so long as it is electrically conductive, and does not need to be ferrous or magnetic. The railgun pushes its projectile forward, unlike the coilgun and Gauss rifle, which pull the projectile.

The principle behind the railgun is the Lorentz force. The projectile in a railgun shorts the rails to each other when it is loaded. When a high voltage is applied to the rails, a large current travels up one rail, across the projectile, and down the other rail. This essentially creates a large loop of high current, and the electromagnetic fields generated inside this loop all oppose each other, pushing strongly on all sides. Since the rails are firmly held in place, the only piece of the loop that can move is the projectile.

Although the forces generated by a railgun are much higher than that of a coilgun or Gauss rifle, there is significant wear on the rails caused by the projectile sliding over them. This is the biggest problem holding back military research into railguns today.

Applications
The most promising application for a railgun is anti-missile defense, as a high-speed projectile fired from either land or space-based platforms could be used to knock out incoming missiles. Space-based railguns would be most useful against ICBMs, which exit the atmosphere on their way to a target. The US Navy is also investigating artillery applications, as a large projectile moving at several times the speed of sound wouldn't even need a warhead to inflict massive damage on a target.

Limitations
A railgun requires extremely high voltages and currents to generate the forces necessary to launch a projectile, although it does so with more force than can be achieved with a coilgun or Gauss rifle. Wear on the rails from the projectile rubbing against them under such stresses is extreme. The plasma flash (spark) generated out the end as a result of the high-voltage circuit suddenly being broken when the projectile leaves the rails reduces efficiency. One last limitation the coil gun and Gauss rifle do not suffer is that the railgun must use some other force, such as compressed air or even gunpowder, to start the projectile moving before the Lorentz force can take over.

Smartalix points out that the rail wear problem could be circumvented if the rails could be manufactured cheaply, becoming a disposable part of the projectile and replaced as part of the reloading procedure.

There is another weapon called a rail gun, or railway gun, although in its case "rail" refers to railroad tracks. During WWII, a type of very large artillery cannon was mounted on rails to transport it from place to place. It was so powerful that its massive recoil made it impractical to fire from a fixed emplacement, so the recoil was instead absorbed by pushing the cannon backwards along the tracks. It was then pulled back into position to fire again.

EMP

Technology
An electromagnetic pulse weapon, or E-bomb, is a bomb designed to generate a powerful electromagnetic field for a short period of time. It does not fire a projectile and does not do its principle damage with a shockwave like a conventional bomb. EMP weapons are harmless to living creatures and most insulating materials, but the electromagnetic field gradient can have a number of harmful effects on electronics, conductive metals, and data storage devices.

A field gradient refers to the fact that the electromagnetic field gets weaker with the square of the distance from the bomb that generated it. This creates a voltage on electrically conductive material that is higher on the near side and lower on the far side from the source of the pulse. This voltage difference causes a current to flow through the material. The stronger the gradient is, the higher the voltage will be and the stronger the current will be.

Conductive metals will heat up, with thin materials perhaps softening and melting or starting fires. Transistors will be damaged by uncontrolled high currents and voltages. Data storage devices will be erased. Power transmission and distribution systems will be damaged by high currents induced in long wires and cables.

Nuclear weapons generate an EMP as a side effect. A pure EMP weapon is theoretically possible by using a controlled explosion to generate a brief, powerful electric current in a large solenoid, which would send out a very large electromagnetic field and probably destroy itself in the process.

Science fiction movies generally show a visible blue pulse wave emanating from the bomb, and state that turning electrical equipment off for the duration of the pulse will protect them. One example can be found in the movie Broken Arrow. Both of these ascertains are untrue. The field itself is invisible to the naked eye, being in the wrong portion of the electromagnetic spectrum. The damage is caused by the voltages induced on the electronics by the field gradient, and it would not matter whether or not the equipment is on. Electrical equipment can, however, be protected by a Faraday cage, as shown in the movie Small Soldiers.

Applications
Disruption of electrical services, knocking out electronics on which modern military vehicles depend, knocking out radar emplacements, knocking out communications, all without harming human targets. However, small pieces of metal carried by a person could heat up as a result of the induced currents and cause burns. Also, medical devices such as pacemakers could be damaged, indirectly resulting in death.

Limitations
EMP weapons are ineffective against electronics which use vacuum tubes rather than transistors, as these devices are far more sturdy. Additionally, low-cost devices such as a Faraday cage could protect certain targets.

Tesla Cannon

Technology
A Tesla cannon does not use a projectile of any sort. The Tesla cannon generates an extremely high voltage, which causes a spark or miniature lightning bolt between it and its target. This weapon is purely fictional, as it would be impossible to aim. An electric spark will always jump from the point of highest voltage to lowest voltage with the easiest available route. The concept is probably based on Nikola Tesla's Magnifying Transmitter.

Applications
None, impractical, fictional device.

Limitations
Impractical, fictional device.

Update!
It may well be possible to aim a Tesla Cannon using a laser induced plasma channel.

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