Maybe, nobody really knows. 300 Whisper/Fireball/221 is a wildcat. Personally I would recommend going with the 300 Blackout ream since it's the new standard.

The Forster 300 AAC BLACKOUT dies are tuned for the Remington factory 300 AAC BLACKOUT cases. Specifically, they don't needlessly overwork the case neck which may extend case life and it may increase accuracy.

Forster not only had the factory cartridge and chamber drawing, but also new and fired cases which helped see the actual neck thickness.