'''5.7x28mm''' is a type of [[ammunition]] for firearms. In real life, this cartridge is considered to be part of the Personal Defense Weapon category, a nebulous category of small, high-velocity cartridges intended for compact firearms. Their primary purpose is to defeat armor; therefore, this caliber is classified in the game as a <span style="color:#AA0000">'''(R)'''</span>ifle caliber, in order for it to have access to rifle-only projectile types and perform the way a PDW cartridge is intended.
Despite being in the <span style="color:#AA0000">'''(R)'''</span>ifle caliber category, magazines containing 5.7x28mm ammunition are treated as pistol magazines in [[load-bearing equipment]].
In real life, this cartridge was originally designed for the [[FN Herstal P90]] personal defense weapon. This was arguably the first purpose-built PDW. It entered in direct competition with HK's [[Heckler & Koch MP7A1|MP7]] and their own PDW cartridge, the [[4.6x30mm]].