Currently reading a book about seafaring in mid-late 1800's. The main ship is about to engage a waters edge fort. Spies report the fort defenders intend to use "heated shot" or cannon balls. The ship captain is much concerned because one of those going into the powder cache will blow up the whole ship. The notion brings up a whole host of questions. Like: how did they heat them so hot as to ignite bp? Or how did they load them without igniting the charge in the cannon? Wads between powder and ball, I'm guessing. Was this a commonly used weapon? etc.