Once you have had a federal license (I maintained one for over fourteen years, buying buttfucking loads of guns and ammo for all my associates and massive quantities of ammunition to feed all those guns in our club - If there was really a problem with the USA FED, I would be one of those who go directly to jail, DO NOT PASS GO, etc ... etc ... etc...), you can still get just about anything, with proper licensing.
Well, there's the rub. You can defend yourself against "ordinary" scum, but you can't defend yourself against your own government if you'd have to, since they know what you own. You could of course take plenty of them out, before they took you, which is a great advantage compared with many countries in Europe, but that is the whole thing what's wrong with licenses in the first place, that they know what people have and can take them out one by one if they would want to.
You could have a light machine gun at home in Sweden too just 15 years ago, if you were a member of the Home Guard. Then a moron, who wasn't a Home Guard man but an army second lieutenant, massacred seven people because his girlfriend had dumped him, and since then they keep all sub-machine guns locked up at the Home Guard stations. I think just some hundred people or so have a license for a private machine gun in this country, most of them (former) cops, soldiers or collectors.
