Possibility of Space Magical Electromagnetic Gun in Bronze/Iron Age

Question

Background

This is a quasi-magical world where sapient species inhabit a range of biomes in a stellar system, from asteroids to gas giant moons to earth-like planets. These bodies have compositions similar to that of solar system. Asteroid biomes are supported by engineered photosynthetic "plants" left by ancient "gods" that are capable of maintaining airtight, pressurised volumes with (handwaved) airlocks and otherwise supporting carbon-based, oxygen-breathing life.

A number of said species are capable of using magic. In the scope of this question, magic has only one use: deliver electric current. A healthy adult of an average humanoid can deliver a very short pulse of ~500J (tentative) by discharging bio-capacitors, and can sustain an output of 200W (tentative) for a minute. For longer timeframe, the average output is ~100W (tentative).

Edit: The short pulse generated is short enough that it can be directly connected to rails (for railgun) to accelerate the projectile without the need of additional capacitors. All the energy numbers above can be increased for at most 200% if it helps, which gives us 1500J/600W/200W.

Question

Is it possible for these species to develop practical electromagnetic guns, somewhere, sometime, before reaching technology level equivalent to 1600s humanity* (in terms of metallurgy, chemistry, fabrication etc.)? If it is possible, how, when and where?

*At which point the earth-based ones should just switch to firearms and cool space magic electromagnetic guns are lost.

Edit: Handheld, one-individual electromagnetic small arms are what I aim for, as they should be easier to manufacture than more complex, crew-served EM guns. Their intended competitors are mechanical ranged weapons such as bows and crossbows, and early firearms like matchlock muskets. More advanced firearms are certainly better than these cruel EM guns, but they should be out of the scope of the discussion.

Electromagnetic guns include coilgun, railgun, reconnection gun and other more exotic varieties. As long as they use electromagnetic force to propel a projectile of significant mass, they qualify.

Supplement: Material

The asteroids most likely contain unoxidized metals that can be readily used. Can these metals, refined with pre-1600s technology, provide adequate materials for construction of electromagnetic gun? One of the concerns I have is electric resistance. Copper is by far the most widely used conductor, but its conductivity is severely reduced if it contains impurities. Can electrolytic copper be effectively manufactured? Is there any other alternative like silver metal in the asteroids?

Supplement: Fabrication

For railgun, the rails seem to require a great deal of surface finish to achieve good contact with the projectile, and making such solid pieces of metal may be a challenge in itself. Similarly, projectiles may require good craftmanship to fit into the rails nicely. (I do not know much about either though) In the case of coilgun, please assume that multi-stage coilgun is possible due to... either the operator discharging several smaller pulses into different wires or some sort of space electric system. Can electromagnetic guns with reasonable performance be produced at militarily-useful quantity?

Answer 1

electromagnetic catapult

For a gun you need a pulse. The 500J pulse won't do much. Also, a "gun" assumes a bullet or cannon ball leaving the weapon at high speed, in a near straight line. That is not always needed to "shoot" and inflict damage. The Roman catapult or glande threw stones and burning substances over walls. In the bronze age that would be a superior weapon of war.

These creatures have one minute 200W power at their disposal, 11.8kJ, enough energy to lift a 50kg object 20 meters up. Now suppose these folks are handy, sapient entities. If you could store the energy in the catapult during one minute, add 100W sustained if needed.. and then shoot. The catapult serves as a spring mechanism, converting the electricity into potential energy.

handhelt coil gun

Suppose they can make copper wire. You'd find a long, straight rod, or reed (say, 50cm) use the copper wire to wind a coil, carefully interspaced with straws and leafs, for isolation. A needle-like arrow is placed inside the reed. The arrow is preferably iron, or bronze cast and polished, with poison on top.

This weapon could be used to hunt larger animals. Also, it could yield a murder weapon that can be used without making any sound.

join forces

They may find a way to join e.g. a thousand soldiers applying their magic electricity skill "in series" or "in parallel", providing way more energy, shooting 3kg cannon balls, like suggested by JBH. With joint forces, a rail cannon may become an option..

BUT

your arrows or bullets are expensive !

For rail guns or coil guns, there better be an abundance of copper and tin available. Else, any projectile of considerable weight would become very expensive to waste as ammunition, in the bronze age. It needs to be made of conductive, solid material.. that is metal. The catapult seems better suited, because the projectile itself needs not be driven by electromagnetic force. you can use stones as ammunition.

Answer 2

No

It's a matter of scale. Let's start with what we know of a working rail gun today:

For potential military applications, railguns are usually of interest because they can achieve much greater muzzle velocities than guns powered by conventional chemical propellants. Increased muzzle velocities with better aerodynamically streamlined projectiles can convey the benefits of increased firing ranges while, in terms of target effects, increased terminal velocities can allow the use of kinetic energy rounds incorporating hit-to-kill guidance, as replacements for explosive shells. Therefore, typical military railgun designs aim for muzzle velocities in the range of 2,000–3,500 m/s (4,500–7,800 mph; 7,200–12,600 km/h) with muzzle energies of 5–50 megajoules (MJ). For comparison, 50 MJ is equivalent to the kinetic energy of a school bus weighing 5 metric tons, traveling at 509 km/h (316 mph; 141 m/s). For single loop railguns, these mission requirements require launch currents of a few million amperes, so a typical railgun power supply might be designed to deliver a launch current of 5 MA for a few milliseconds. As the magnetic field strengths required for such launches will typically be approximately 10 tesla (100 kilogauss), most contemporary railgun designs are effectively air-cored, i.e., they do not use ferromagnetic materials such as iron to enhance the magnetic flux. (Source, emphasis mine)

That's five million amperes for a few milliseconds to produce 5-50 megajoules.

And your creatures are producing 500 joules.

To be fair, Wikipedia is talking about a naval canon.

In 2010, the United States Navy tested a BAE Systems-designed compact-sized railgun for ship emplacement that accelerated a 3.2 kg (7 pound) projectile to hypersonic velocities of approximately 3,390 m/s (7,600 mph; 12,200 km/h; 11,100 ft/s), or about Mach 10, with 18.4 MJ of kinetic energy. It was the first time in history that such levels of performance were reached. They gave the project the motto "Velocitas Eradico", Latin for "I, [who am] speed, eradicate"—or in the vernacular, "Speed Kills". An earlier railgun of the same design (32-megajoules) resides at the Dundrennan Weapons Testing Centre in the United Kingdom. (Ibid.)

So we're sending a 3.2 kg object into the air. Let's scale that down (I'm really simplifying things doing this, but it'll make the point). Depending on the gun, the mass of a bullet usually ranges between 0.02 kilograms and 0.04 kilograms. let's use an average of 0.03 kg and that gives us a linear scale of 107:1.

50 megajoules / 107 = 467 kilojoules, which is still a thousand times greater than the 500 joules your creatures can produce.

So I regret to inform you, there's no hope that your species would develop electromagnetic propulsion of any kind with their current abilities. I'm afraid 500 Joules wouldn't create an electromagnetic popgun.

Having said that...

Getting a thousand of your creatures to proverbially hold hands to launch a single projectile seems impractical to me... but if you scaled their power-generating abilities to 50,000 joules such that only ten were needed. That's where I could suspend my disbelief to enjoy the story. Remember, you're only launching a rifle-bullet-sized projectile (so it's still somewhat impractical), but the team effort now adds a cool dynamic to the story.

Errata:

Thanks to @RedMoon for pointing out some more analysis. In the end (you can look at the comment chain), an "average" hunting rifle is expected to drive 1,800 joules of energy at the target. The closer you are to the target, the closer you are to muzzle energy, so that 1,800 is the lowest value. But if we use that as the best-case (lowest necessary value), we're still 3X+ over what the creatures can generate.

The massive discrepancy between the approximated muzzle energy of a hunting rifle and a scaled version of the Naval rail gun (scaling down from 3,200 m/s to 1,200 m/s) leaves us with a rail gun needing 150 kJ compared to 1.8-18 kJ. That suggests rail guns are a mite inefficient, which to my Electrical Engineering spidey sense, actually makes sense. What makes them valuable is that a nuclear reactor can generate the necessary energy at a much, much lower fuel density than the same delivered-damage of chemical weapons.

But, good news! Now we're down to 3-4 of the creatures chaining together to make the gun work. That's cooking with gas in my book!