What, exactly, makes the Five-Seven different from other handguns? The Five-Seven is chambered for the 5.7 x 28mm cartridge, ammunition originally developed by FN Herstal for the FN P90 Personal Defense Weapon. The P90 was conceived as a compact, powerful weapon that could be carried by aircraft crews, vehicle drivers and other troops who needed a weapon that was smaller than a carbine but larger than a pistol.