The Puckle Gun was invented in 1718
Hell, Leonardo da Vinci designed a rapid fire gun in the 14th century (never built, but on the drawing board).
I believe that our founding fathers were very forward thinking people, so I think you'd be amazed what they envisioned for the future.
One thing our founding fathers VERY CLEARLY though about was the totalitarian impulse ... which they designed our entire form of government to resist. And to quote Al Sharpton; "Resist we much!"