This question might involve too much current for an electronic engineering board, but it involves electricity, so I'll ask it anyway.
YouTube videos of the railgun https://www.youtube.com/watch?v=ZL4kbBIf39s show a curious phenomenon; billowing clouds of what appear to be flame emerging from the barrel. Those are understandable from conventional cannon, because there is combustion continuing after the projectile leaves the tube, but railguns don't use combustion.
What's going on? They're far too fractal to be supersonic shock waves. Are they plasma, glowing atmosphric gases that have been heated by compression in front of the projectile, or something else?