I don't believe they can legally pass a law to confiscate anything. There is a clause or two in the constitution which prohibits Ex Post Facto laws. In other words they cannot pass a law that makes something you did (or own) illegal if it was legal when you purchased it. Even if they can pass a so-called "assault weapons ban" (Which I doubt they can) I am pretty sure that anything you already own would be grandfathered in just like the last time. They would like to do a lot of things that they cannot do. Thankfully we have a constitution that prohibits much of the nonsense you keep hearing about.
How does that reconcile with the bump stock ban ?