The .224 Boz cartridge was developed in the late 1990s, designed as a candidate replacement cartridge for adoption as the standardized NATO ("STANAG") Personal defense weapon PDW round, originally solicited to replace the longstanding NATO standard (STANAG) 9ÃÂ19mm Parabellum. It was going to be the British entry, to be evaluated alongside the Belgian FN 5.7ÃÂ28mm and the German HK 4.6ÃÂ30mm armor-piercing cartridges. The solicitation would also seek to find, test and standardize a PDW cartridge capable of, at the minimum, defeating the Collaborative Research Into Small Arms Technology (CRISAT) body armour of the time.
The .224 Boz began as a 10mm Auto case necked down to . Original trials were successful, with this round firing a projectile chronographed at over . During development a version based upon the 9ÃÂ19 Parabellum case was also evaluated, which carried the significant advantage of being able to be utilized in pre-existing NATO standard 9ÃÂ19 Parabellum caliber firearms by means of a relatively cheap barrel and caliber swap. The .22 TCM takes advantage of this same concept in its sub-variant, the .22 TCM 9R.