So I've been considering for a long time getting a 30 cal can and doing a 300 Whisper upper. Of course now that the Blackout allows the whisper its looks even more attrative. From what I understand the big difference is the whisper was a wildcat off the 221 case, the Blackout is SAMI offical and high FPS but can still fire the whisper. My guess is is anyone using 223 cases yet and is it using a standard 308 projectile?