Just what is an "illegal" gun. Obviously the gun itself cannot be illegal. What makes a gun "illegal" is human action.
What is an illegal gun? Let me count the ways.
1. A gun in the possession of a law-abiding citizen.
2. An unregistered gun.
3. A gun used in self-defense.
4. A gun collected as a hobby.
5. A gun used for target practice
6. A gun used in any sport
Get it?
The goal is to make the possession of a gun illegal.
If I moved from Pennsylvania back to New York State, I would change from Responsible Citizen to Dangerous Person. :-(