Well, several things:
A) Constructive Intent... ever heard of it? It's a goofy part of the WA State Law that says that you are not allowed to own a part that is designed exclusively for use in a machine gun. I.E. A 3-shot burst kit, an auto sear, an M-16 full circle bolt carrier etc., etc. Regardless if you have it installed or not it is still a felony. Regardless of the fact that non-Class III dealers sell them at the gun show to anyone who will buy them. Still a felony. The reasoning (however stupid it is) is that the state feels that the ONLY reason you would have a part soley for use in a machine gun is because you INTENDED to build a machine gun... and that in and of itself is a crime in their eyes. Even if you didn't have ALL the parts necessary to finish the gun. Provided that you have a 3-shot burst kit and even a stripped AR-15 lower that is enough to get popped.
Of course if you only own a Steyr AUG or FN FNC then you could have all the M-16 parts you wanted... even the auto-sear.
Of course their are some exceptions:
1) You are an 01/03 FFL (Class 3 Dealer) or
2) You are an 07/02 FFL (Class 2 Manufacturer) or
3) You are one of the lucky few in WA that has a Pre-1994 grandfathered machine gun legally registered with the ATF or
4) You don't own an AR (see example above) and
5) You intended to sell them only to people that met the above criteria.
.... but you didn't mention that.... so I assumed you did not know. Perhaps I jumped to conclusions. Or perhaps I have helped educate the greater AR-15 community about the whacky WA laws.