[9thLife]

Where is all the flame coming from, if exposives aren’t involved in propulsion?

[Steely Tom]

Where is all the flame coming from, if exposives aren’t involved in propulsion?

It's what's left of the arc that is formed across the rear of the projectile (or maybe across the entire projectile in this case) following it as it leaves the mouth of the launcher.

[Tonytitan]

Where is all the flame coming from, if exposives aren’t involved in propulsion?

Where does all the flame come from when a lightning strike starts a forest fire?

[Slambat]

“Where is all the flame coming from...”

I think there is some sacrificial skids or rails
that holds the projectile as it’s accelerated on
the guns rail or rails. I would assume there would
be a little friction going from 0 to mach 6 in just
a few feet.