Common sense is usually the best thing. . If you possess a firearm that you are not licensed to possess, then you are illegally possessing a firearm. A felon can not possess a fire arm. There are other restrictions as well. Military weapons (actual automatic weapons etc.)  are only allowed to civilians with special permits. If you steal or have in your possession a stolen weapon, once again illegal.

 I don't even have a problem with a no-buy list. As long as certain come with it. 1) notification that you are on the list within 10 days. 2) A hearing before a judge to explain why the government feels that they have to prevent you from  a Right. 3) A civilian over-site committee in each county to over see all aspects of the program with the power to over rule the local judges decision. 

Our Constitution does not grant us anything. What it does is acknowledge that man has certain inalienable rights. One of those is in the 2D. The right to self defense.