$ 2.95  per cartridge
Current Pistol & Rifle Cartridge Section
.221 Remington Fireball
Picture on the left,
.221 Remington Fireball
factory loaded by
Remington, using a  grain
Jacketed Soft Point, 22
caliber projectile.
Also pictured:
(A.) 221 Fireball
(B.) 222 Remington
For size comparison.  
Due to the demand for varmint hunting and silhouette shooting, the .221 Remington
Fireball cartridge was introduced by Remington in 1963 for the (then new)
Remington XP-100 Pistol (now obsolete firearm).
The cartridge is based on a shortened 222 Remington cartridge with a .22 caliber
projectile, velocity of (up to) 2650 Feet per Second and
(up to) 765 Foot Pounds per square inch of energy, "that is over the 357 Magnum".
Some also consider this a rifle cartridge.