How do you get 50 rounds in a gun without having the magazine catch on anything? You move the magazine above the axis of the bore. Fabrique Nationale introduced the innovative 5.7x28 mm cartridge back in the early 1990s in its selective-fire P90. It was intended to be a whole system designed around what is really a little miniature version of the 5.56x45 mm NATO cartridge. The closed-bolt, blowback-operated P90 is complete system that fulfills the role of the original U.S. M1 .30 Cal. Carbine. These days, it is concept called the Personal Defense Weapon (PDW).
What the 5.7x28 mm delivers is penetration, accuracy and light weight, all while being very controllable in full automatic. The P90 in its military and law enforcement guise is capable of selective fire, meaning either semi-automatic or full automatic. It takes a 50-round-capacity polymer magazine that is simply ingenious. The cartridges are actually mounted sideways in the magazine and take an abrupt 90° new turn as they are presented into the feedway. The fully ambidextrous, bottom-ejecting P90, of course, is a bullpup design making it compact and portable. Really an ideal arm for say an armored vehicle crew to use in the event they had to bail out of their vehicle, which was its intended role. Now, it is also used as a dignitary protection arm, including use by the U.S. Secret Service.
Ballistically, the 5.7x28 mm is essentially rimless .22 Hornet, with a 40-gr. bullet moving at more than 2000 f.p.s. The original cartridge as conceived by FN was for use by modern military forces and employed a penetrating round that was capable of defeating body armor. That round is not available to civilians in the United States. Instead FN has created a round designed specifically for civilian use.
FN USA offers the semi-automatic-only PS90 with a 16-inch barrel commercially in the United States, as well as the Mk V version of the Belgian-made FN FiveseveN pistol. While we fired a suppressed version of FiveseveN pistol while in Belgium last week, the gun being fired in the accompanying video by American Rifleman Television Field Editor Martin K.A. Morgan is, of course, the military and law-enforcement-only version of the selective-fire P90. Watch video below of Marty firing the gun.