It looks like the approval of Form 1's to manufacture SBRs in WA was very short-lived. It appears that the ATF is using a loophole in the RCW because the RCW doesn't explicitly say "manufacture" although "acquire" and "possession" are ok. No word if an FFL can build it and transfer it. 

Rcw 9.41.190

(2) It is not unlawful for a person to possess, transport, acquire, or transfer a short-barreled rifle that is legally registered and possessed, transported, acquired, or transferred in accordance with federal law.