all issues with printing firearms aside, this is pretty clearly an exercise in futility. Zip guns/homemade one-off pistols have been available for as long as firearms have been. At it's core you can have a tube, capped off at one end with a wick or blast cap igniting gunpowder in the back and shrapnel in the front as a homemade blunderbuss.
All you need to really make a zip gun is a nail, a tube of applicable size, and possibly a sabot to house the round, it's not difficult. At the end of the day the bullets are the big problem, and they're readily available, and not especially expensive.
All this is, is a civilized zip gun. They will never fully remove this or any other homemade weapons from existence. Where there is a will, there is a way. Regulations can be attempted, but at the end of the day, they're just throwing tax money down a rathole, fighting a war that cannot be won.