Is the Fireball its own animal or based on another case?
If by "it's own animal" you mean wildcatted from a SAMI cartridge....no...
It was a factory round developed by Remington for use it it's single shot XP's...
If you're asking if it was based on another cartridge...yes...
It's a shortened 222...but you could basically say any of the .378 dia. cartridges are "based" on the original 222...
https://en.wikipedia.org/wiki/.221_Remington_Fireball
