“The earliest example I know of comes from the days of warships with sails and black-powder cannon. Two cannon balls joined by a length of chain were fired into another vessel’s sails These would cut ropes, entangle all sorts of rigging, and possibly bring down masts. “
As I understand, this was often done with two cannons, not two balls in one cannon. I imagine a misfire or late fire on one could have disastrous effects.
Only in the mind of a movie director with no experience of firearms.
At the time, cannon were relatively new and were the subject of investigation by the most advanced scientists and mathematicians alive at the time. The synchronization required would easily be shown to be pushing the limits of any technology. Even if the first shot went well, disaster would soon occur.