It is 1861. A man named Dr. Richard J. Gatling is inventing a complex engine of ballistic destruction ironically, Gatling claimed, to reduce the size of armies and therefore reduce the deaths in combat and to show how futile war was. And so, during the civil war and many times from then on, people actually got attacked by these things. I cannot fathom how Gatling could not have guessed people would just send in more soldiers to get shot up.
A British 1865 Gatling gun at Firepower – The Royal Artillery Museum
Here is the crazy part: because the original Gatling gun was hand-cranked, it is not technically an automatic weapon and is therefore theoretically legal. I would imagine that it would be hard to acquire one though. What reason could you possibly have for wanting one? What would you use it for? Hopefully not hunting, although that would be the only legitimate reason. Protecting your home? It’s got to be very expensive to buy ammunition for this thing, and I read that it takes a very long time to set up. I suppose the only way you could get one is if you could somehow convince the seller you were not going to use it for the only thing these guns are rightfully for: shooting at nineteenth century cowboys.