What's darkly funny to me is that those things are illegal. Perhaps the biggest event in favor of keeping such weapons outlawed was the North Hollywood shootout (http://en.wikipedia.org/wiki/North_Hollywood_shootout, basically IRL Payday), and yet only two people--the robbers--were killed!
Actually not. Only ones manufactured after 1986; there are roughly 250,000 in private circulation (and I can dig up a current case where a police department is selling a vintage 1920s Thompson sub-machinegun so they can buy stuff they need).
ADDED: per the NRA's page on California gun laws, in theory its even legal to have and transport one, although evidently the permits to do so are never granted (well, I assume except for Hollywood...).
2 known illegal uses of legal machine guns in private hands in the US ... one by a cop....
