Ca started this ex post facto tactic in violation of the constitution and they were allowed to do it so now everyone is following suit.
That is the common-sense understanding of Ex Post Facto.
The courts have rules something different. It goes like this:
You cannot be fined or imprisoned for having x before this date, because that would be Ex Post Facto.
Now that the law is changed, you can be fined for having x after this date, because the law has changed.
You are not being fined for having it then; you are being fined for having it now.
It used to be common sense, that if you owned it legally, and the government made it illegal, at minimum, they had to reimburse you for it.
Not any more.
And the courts have distorted it, example seat belts, They passed the seat belt laws. But under Ex Post Facto these laws could only be required for all new vehicles being produced after it was passed. Vehicles that were already sold, owned, produced, could not be required to retrofit seatbelts. And tickets cannot be written for not wearing seatbelts in a vehicle that was not required to have seatbelts because it was produced before the law was passed.
It is still this way with seatbelts and it is the constitutional way because Ex Post Facto applies and is observed. It is already this way with many firearms and parts and has been for years now. Based on Ex Post Facto, they can only restrict future manufacturing, imports, or sales. Not those already sold or owned legally. “Pre-ban” is a very common term with firearms and parts because based on Ex Post Facto pre-ban are still legal.