A movie (possible tv series), that ended with an iron clad boat with explosive cannonballs that would be ignited by a orange glowing cannonball, pretty sure it was live action, but not sure. The rest of the movie may or may not have been steampunk. I'm pretty sure the boat was about to fire upon a city before the hero stopped it.
not really steampunk but you could get that vibe maybe Jonah Hex.
Boat and city at the end.
Orange cannon ball things.
Maybe steampunkish if you squint -shrug-