Consider using instead the realtively new 300 AAC Blackout. The 300 Whisper, 300-221, 300 Fireball, and the 300 AAC BLACKOUT are all of the same vein. They all use a .223 or .221 cartridge and neck it to a 30 caliber bullet. The only difference is that the AAC BLACKOUT has been submitted to SAAMI for standardization.
Which means, you will be able to get FACTORY LOADED AMMO (Right now produced by Remington) and factory brass for reloading as well.
The main differences that I have seen in the discussions and the comparison is the throat length.
The nice thing about this cartridge is the fact you can load it with 220gr bullets and shoot them subsonic making it a nice PDW type firearm and suppressor friendly.
You can also load this with lower grain bullets and have a pretty effective deer rifle out to about 200 yards or so, depending on your confidence.
There has been a lot of discussion on this round, including chamber reamers that can convert the other 300-221 based rifles to this new standardized caliber on
www.silencertalk.com
There are dies available from Forester. You can use a .308 Crimp die cut down to work with the shorter round. (I'm uncertain how much needs to be cut off just yet, but I'll figure it out based on the case length differences.)
I'd hate for you to spend money on a round that has been newly standardized. (Or will be newly standardized in the very near future.)