The Puckle gun was fired in a similar fashion to a conventional flintlock musket; however, after each shot, a crank on the threaded shaft at the rear would be unscrewed to release the cylinder to turn freely. The cylinder would then be advanced by hand to the next chamber, and the crank turned back again to lock the cylinder into the breech of the fixed barrel. The flintlock mechanism could then be primed for another shot: it was triggered using a lever which was separate from the crank assembly.
To reload the weapon, the crank handle could be unscrewed completely to remove the cylinder, which could then be replaced with a fresh one. In this way it was similar to earlier breech-loading swivel guns with a detachable chamber which could be loaded prior to use. The cylinder appears to have been referred to as a "charger" in contemporary documentation.[2]
This is obviously a lower rate of rounds per minute than modern semi-automatic rifles are capable of, yet if the founding fathers knew of the existence of this technology, don't you think they could have foreseen the advancement to what we have now? They were, after all, a bunch of inventors.
Maybe they did know or maybe not, I for my part had never heard of this weapon, which I doubt was much used, it was British and they had a tough time winning any wars in that century.