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) 9×19mm Parabellum. It was going to be the British entry, to be evaluated alongside the Belgian FN 5.7x28mm and the German HK 4.6×30mm 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.^[1][2]

The .224 Boz began as a 10mm Auto case necked down to .223 in (5.7 mm). Original trials were successful, with this round firing a 50 gr (3.2 g) projectile chronographed at over 2,500 ft/s (760 m/s).^[3] During development a version based upon the 9x19 Parabellum case was also evaluated, which carried the significant advantage of being able to be utilized in pre-existing NATO standard 9x19 Parabellum caliber firearms by means of a relatively cheap barrel and caliber swap.^[4] The 22 TCM takes advantage of this same concept in its sub-variant, the 22 TCM 9R.

• .22 TCM
• .22 Spitfire
• HK 4.6×30mm
• 5.7×28mm
• Table of handgun and rifle cartridges