In early experiments in the development of the SCAMP machine pistol's ammunition, the engineers originally tested the .223 Remington round. However, it proved to be too powerful, thus they experimented with other small-caliber rounds, such as 9×19mm Parabellum, .22 Winchester Magnum, 5mm Remington, .22 Hornet, and .22 Long Rifle.
The design team eventually settled on the .221 Remington Fireball as the basis of the .224 caliber centerfire cartridge, the .22 SCAMP.
The SCAMP round had a 40 grain bullet which traveled at a muzzle velocity of 2100 feet per second. Testing showed that the new round shot flat and accurate out to about 125 meters, far superior to most military pistols of the time.