Well . . . WA law requires (note the word "requires" there, not allows or permits) the FFL to give you the rifle after 10 business days, whether they have heard back from law enforcement or not.
But, with that said, many FFLs do not follow that law, and there's probably not a hell of a lot that you can do about it. My only recommendation would be to choose your FFL wisely for all purchases or transfers, and ask before you buy.
This is one of those things that you can write off as "no big deal" if it's 10 days, or 14 days, or 20 days. However, sometimes it takes weeks and weeks for law enforcement to do it, and you can just be held hostage.
So for the next gun, choose wisely. We have a thread on FFL policies here:
viewtopic.php?f=51&t=105884If you can provide input to that thread based on your experiences, it would be appreciated.