I'm guessing the firework didn't go out of the tube because it wasn't on a stable launch pad, then it blew up in the tube.
I would think it's more likely the shock caused internal brain injury than it blew his head off. This is all just speculation though. It would probably peel your wig back at the least.
I would lean more towards the concussive blast from the mortar needing to be launched from the tube far out into the air crushed the fuck out of his skull and or snapped/ripped his neck open. Best case it probably stomped his head into a mud hole.
“Devon was not the kind of person who would do something stupid,” Cody told the New York Daily News.