I have never TRIED to grow osage but we have butt loads of it around here. Most of it is only fit for firewood but occasionally I find some that is straight and bow worthy. In my search for good osage I have made some observations that may prove to be helpful.
It does no good to grow it on purpose unless you can also grow it straight. So that means that you will need to stake it and prune it as it grows. Also keeping it a little bit in the shade of larger trees will make it fight for light and want to grow straight. the other thing is to make sure that it is somewhat protected from prevailing winds so that it doesn't develop twist.
Thick rings are produced by an abundance of moisture and nutrients so keeping it faithfully watered and fertilized should help it put on mass quicker. I have no doubt that it would grow well in Wash or Oregon doesn't everything? It is gonna want to put on alot of thorny branches early as a protection against things that might want to destroy it so it will take some tending to but I think it can be done.
I can say this though, I'm glad I don't have to worry about it. I just need to find some creek bottoms near pasture that has hedge rows and then find out who owns it to gain permission to cut some if i find any thats worthy to be made into a bow. Danny