My mom was and is pro gun control, and consequently, I have been watching the fate of gun control legislation since I was a child. It is a sad activity.
The only gun control control legislation that both become law and survive court challenges are those that are stupid and ineffectual ones. This is not because gun control advocates are stupid, though of course some are, but because the gun lobby and the NRA play excellent defense both in the legislature and the courts.
Example, back when I was a kid, here in California gun control was popular and gun control measure were passable. So California would pass laws using standard industry term, and they would go to the courts and the industry lawyers would say that they didn't know what these terms meant and maybe they meant this and maybe they meant that, and ultimately the the judge would throw out the law as being to vague unenforceable. So the legislature responded by getting very specific in their terms, and the gun lobby loved this because it allowed them to redesign their products and by making small modifications they could make them legal and force there customer base to buy the modified version of the gun and thus increase their profits.
So, WA passing a stupid and ineffectual law that goes well short of banning and seizing all semiautomatic weapons, and will probably die in the courts anyway,iti does little convince me that tough, large scale gun control is politically feasible.