Ok i have a question, if i ordered a 300 blackout in the 9" range, can you make it function with a adjustible piston upper? Also is the case dimentions the same as a 300 whisper/fireball/300.221? 1-8 or 1-9 twist will work.
You should be able to make it work with a piston conversion if you can shorten the piston to be a 'pistol' length gas. It won't be drop in. But someone can make it work.
As for the case, if you agree that a 300 Fireball is just a 221 Fireball opened to .308 cal - then yes, they are pretty much the same. The headspace is the same. As for the chamber, no the chamber is not the same as the 300 Whisper(TM)/Fireball/30-221. The 300 AAC BLACKOUT has a longer throat which allows bullets to be seated to full magazine length, and this has the benefit of allowing for more velocity while staying within a given pressure limit. Think of it as like comparing a 5.56mm chamber to 223. This also means that if you load 300 AAC BLACKOUT ammo to 55,000 psi and shoot it in a Whisper chamber, you would probably get pressure over 60,000 psi - which would be above SAAMI specs.