Its just either completly ineffective, or effectively bans 3d printing. Then you are going to run into enforcement, and legal challenges. Oh and even if all that is done guns will still be present at a ratio above 1:1 in the states.

Anyone who has a highschool level of metal shop can also make a firearm, 3d printing is not even well suited for the task. Just look at Japan, one of if not the most restricted nation for firearms, and someone shot a leader with a homemade firearm.