designed to fire the FN 5.7×28mm cartridge which can penetrate soft body armor. The P90 was designed to have a length no greater than a man's shoulder width, to allow it to be easily carried and maneuvered in tight spaces, such as the inside of an armored vehicle. Introduced in 2001, the Heckler & Koch MP7 is a direct rival to the FN P90. Featuring a more conventional-looking design, the MP7 uses a short-stroke piston gas system as used on H&K's G36 and HK416 assault rifles, in place of a blowback system traditionally seen on submachine guns. The MP7 is able to use 20-, 30- and 40-round magazines and fires 4.6×30mm ammunition which can penetrate soft body armor. Due to the heavy use of polymers in its construction, the MP7 is much lighter than older SMG designs, weighing only with an empty 20-round magazine. Applications The PDW concept has not been widely successful, partly because existing PDWs are not significantly cheaper to manufacture than carbines or full-size military rifles. Most PDWs also use a proprietary cartridge, such as the 5.7×28mm cartridge for the FN P90 or the 4.6×30mm for the H&K MP7, neither of which were originally compatible with any existing pistols or rifles/carbines. Although both manufacturers planned handguns that used the same proprietary rounds, only FN went forward with production of the Five-SeveN pistol, which was the only handgun option available for the 5.7×28mm cartridge for over two decades until the introduction of Ruger-57 in 2019. In turn, this made the PDW cartridges expensive to consumers due to the lack of mass production. A different take on the PDW concept is the Russian-made PP-2000, which can fire common 9×19mm Parabellum ammunition or a special high-pressure armor-piercing variant to give it similar capabilities as other PDWs. Though personal defense weapons have not been very popular for their intended application, they have been acquired by many special forces and law enforcement groups as direct upgrade for submachine guns. The FN P90 and Five-seven pistol are used by military and police forces in over 40 countries throughout the world, including Canada, Cyprus, France, Greece, India, Peru, Poland, Spain and the United States. The Heckler & Koch MP7 is also used in a number of countries, including Austria, France, Germany, Ireland, Norway, Malaysia and the United Kingdom. Modern PDW cartridge FN 5.7×28mm HK 4.6×30mm 5.8×21mm DAP 4.38×30mm Libra 6.5×25mm CBJ 5.56×30mm MINSAS 7.5