221 fireball is the parent cartridge of the 300 Whisper and 300 Blackout. Somewhere prior to the introduction of the 300 BO there were 300/221 die sets offered by Hornady and custom contender barrels in 300/221 by various makers. The 300 Whisper is a proprietary round hence manufacturers other than SSK using the 300/221 nomenclature so old JDJ wouldn't sue them.
