That line was destroyed last week by the shooting in Florida.
Public opinion has shifted pretty dramatically, I don't think it will stop. (ETA: The "enthusiasm gap" has always been in favor of firearms-rights advocates. That's probably the biggest change resulting from Florida. Firearms right advocates can no longer assume they have an edge in enthusiasm. Time will tell)
As for removing certain guns from circulation, slow is not at all bad. Ban legal manufacture and importation. Such weapons seized by police due to use in criminal acts get destroyed, not auctioned off. The supply starts to dry up. Guns can last just about forever, but not all of them do.
If you want to ban a given type of gun in it's entirety (I generally think that's a bad idea, but...) there are ways to make it happen.
- Order them to be turned in, you might be surprised by the number who do it voluntarily.
- Allow a long grace period where police would seize one if they encounter it but would not seek them out, and the owner would not face prosecution for having it (ETA: unless the owner was already otherwise prohibited from owning firearms).
- After that, there would still be no prosecution for turning them in, ever, but it a person could be prosecuted if they somehow get caught in possession of one - but still no active seeking out.
Use the background check system for that to start building a registry.
- Modify the system so that ALL gun transfers (sale, trade, inheritance, gift) require a full background check, with the type of gun included as a component of the information entered.
- That information is retained and becomes the basis of a registry
- Grandpa does not need to register his duck gun in the closet, but once you inherit it, it you get a background check and it gets registered that way.
- The system builds gradually.
- That's illegal under current law, but opinion is shifting fast and laws can be changed
.
You can dry up and severely reduce the supply without targeting them for seizure.
That said, I have doubts about any sort of plan that involves a full ban on anything currently in circulation. I can support banning manufacture and import of new weapons or accessories of this or that type and letting the supply slowly dwindle.