Jeepkid...
I would venture to say the 17 Fireball is a necked down version of the old 221 Remington Fireball( which is a shortened version of the 222Rem)case, not the 223. The "new" 17 Rem Fireball is real simularto the wildcat 17 Mach IV. I could be wrong about this though, I havent seen much on the 17 fireball.