Printed plastic “guns” are a fucking joke. That’s because any plastic that a 3D printer can print with is way way way too weak to contain the energy produced by the burning powder sufficiently to impart significant force onto a projectile.
In order to make a firearm, you want metal. Some pieces of steel plumbing pipe from the hardware store will work far better than printed plastic. It’s been possible to make firearms from that ever since hardware stores have been selling steel pipe. The result is called a zip gun.
Read what I posted back in 2013 first (including the linked article) before you run off the rails about either a new level of threat due to unregulated gun ownership or a new level of liberty due to the newfound impossibility of regulating guns.