Square Bullets, Revolver, Machine Gun Flintlock, and rapid fire are just some words describing what is known today as "The Puckle Gun" that was built and patented by James Puckle in 1718. With a fire rate of approximately 9 shots per min (compared to the average infantry man at 3) firing out a bore in excess of one inch the results could be devastating. Devastating results were "improved" upon with the option to fire square, yes square bullets.
Why square bullets? The answer was "simple" in that those would be reserved for Muslim Turks in the effort to "convince the Turks of the benefits of Christian civilization".
Little more than pictures and information have been gathered at this point. There are a fair number that have been built by individuals as a simple internet search will show. Most all employ an ignition system like that of a cannon and not a flintlock. This lock will be the most difficult piece to make and will take time as it will require building from scratch.