"Assault" weapons bans

Excess stocks of turn of the 19th Century bolt action rifles were converted to emergency issue light machine guns in WWII with a few simple machine shop parts... It's very easy for a determined psychopath to do this. Rigging forward pistol grips or fold down stocks is trivial. There's nothing too complicated about making extended capacity magazines either. Jewish resistance fighters in the Warsaw ghetto made submachine guns out of plumbing parts. It's very rare indeed that a major shooting incident is the result of someone "Just snapping" they've been planning it for months, even years. Guns were invented, there's no putting the genie back in the bottle. All you can do is frustrate the hell out of enthusiasts while barely hindering the criminals and psychopaths. Doesn't matter if you make some collection of trivial gun features super double secret illegal or not, the "wrong hands" will find a way to get it.

couldn't you make a little electro-mechanical device that, upon pulling the trigger, rapidly wiggled a lever back and forth?

screw that to the trigger guard and, when you pull and hold the added trigger, the gun's trigger gets squeezed by the wiggly lever rapidly enough as to make it functionally automatic.

mass production should be possible, even on the sly, mainly out of plastics? or, surely you could cannibalise something so simple from another cheap device and simply attach it to the trigger-guard?

so, yeah, i'd have to agree.