A journalist for Mother Jones explains the process in the video above.
Although US customs laws ban importing the weapons, parts kits—which include most original components of a Kalashnikov variant—are legal. So is reassembling them, as long as no more than 10 foreign-made components are used and they are mounted on a new receiver, the box-shaped central frame that holds the gun's key mechanics. There are no fussy irritations like, say, passing a background check to buy a kit. And because we're assembling the guns for our own "personal use," whatever that may entail, we're not required to stamp in serial numbers. These rifles are totally untraceable, and even under California's stringent assault weapons ban, that's perfectly within the law.Here's a field test of a similarly-assembled weapon:
Via The Dish.