[Isk]

I am not sure what Washington law allows an officer to do in regards to your firearm, but I wouldn't be too concerned about whether the law allows the officer to secure it. As a general rule, always follow the orders of a law enforcement officer. If he wants it, turn it over. If you think he doesn't have the right to secure the firearm, I suppose you could make a simple statement ("I don't believe state law allows you to do that, but here you go"), but you certainly don't want to spout off about how you are protected by the Fourth Amendment and you "know your rights". Cops hate that and it only leads to headaches.

Constitutional questions are resolved after the fact, with a supervisor or through the courts.

Also, if the officer wants your gun, I'm inclined to allow him to remove it instead of handing it to him...I wouldn't want any confusion on that issue. Hands should never go near a firearm when law enforcement is being dealt with.