is there any means by which the passage of new federal “assault weapons” ban could result in the confiscation of firearms purchased before the passage of the bill as was done in the UK and Australia?
YES, absolutely, if the bill is written as to allow it. The 1994 Fed law was written to grandfather in existing guns. It also had a sunset provision. State versions of the same law, did not, and are still in force.
Ex Post Facto seems to be a principle ignored in (some of) these bills. Look at the history of the CA laws. They passed laws requiring the registration of certain "assault weapons", guns owned and purchased BEFORE the registration law even took effect. And the law allowed the CA AG to determine which ones (and when) were no longer legal to own.
Guys that complied with the registration (because if they didn't register them, they became illegal), got to own their guns for another year, or three, then, later, when the AG decided they were no longer legal, they had to turn them in. And because they were registered, they knew who complied with the surrender order, and who didn't.
AND, to top things off, some of the people who complied, and turned in the guns were charged with having illegal guns, WHEN THEY TURNED THEM IN!
remember, "if I could have gotten 51 votes, Mr & Mrs America, turn them ALL in!" Came from a CA politican. And she's STILL in DC working hard for "our best interests".
There's people from every state with that mindset. Just because they aren't pushing their agenda hard right now, doesn't mean they have given up and gone away.