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.
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.
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?
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?