Forgive me for saying so guys, but none of those type of laws will be effective.
The truly mentally ill will find a way to get destructive devices to kill people with anyway.
The government finds a way to restrict guns to more people, but the people they stop with it aren't the ones who are committing these acts. The people who are that sick do not care about breaking the law to accomplish their purpose. They will lie, cheat, steal, and kill to accomplish their goals. This can't be argued. Keeping them form buying guns at the counter at Cabela's probably won't even slow them down.
Let's say it works and they can't buy guns, it won't, but let's just say. No problem, they'll find something else I promise, and the first one to use some horror that works effectively will be imitated.
Gaily bedight, A gallant knight In sunshine and in shadow, Had journeyed long, Singing a song, In search of El Dorado