A railgun, while its mechanism is electromagnetic, works on a base level by causing a massive high-current electrical short. As a side effect (as in most elect

A railgun, while its mechanism is electromagnetic, works on a base level by causing a massive high-current electrical short. As a side effect (as in most electrical shorts), both the rails and some of the projectile are vaporized when the gun is fired due to both friction and electric arcing; and that's the smoke and fire you see. This wear (which is signifcant per shot) is also the main obstacle to actually using railguns in any significant capacity in warfare (the other being the need for a massive current source, but nuclear generators and massive capacitor banks help). Coilguns, on the other hand, don't actually touch the projectile they fire, and as such have a significantly cleaner output.