Legal ownership requires FFL/SOT licensing, strict ATF compliance, and usually six-figure prices.
six-figure prices
For an uncontrollable automatic handgun that holds a max of 33 rounds? Why bother. For that kind of money you can probably pick up a full auto MP-5 submachine gun and actually have something that's more reliable and controllable. If you're going full auto, pretty much have to have a stock or brace of some sort of you want your fire to be effective.