JS-9 = Chambered for the .9x19mm-Parabellum cartridge, new standard sidearm ammo for the PLA. This submachinegun can take any world-manufactured .9x19mm-Parabellum round, but is optimized for the armor-piercing DAP-92 cartridge, this being by itself a Chinese copy of the Russian .9x19mm-Parabellum PBP ammo developed for the GSh-18 pistol (the Russian PBP and Chinese DAP-92 cartridges take their special armor-piercing capabilities not only from their specially conceived bullet, as described by Mr. MAXIM POPENKER at
http://world.guns.ru/handguns/hg111-e.htm , but also from their extra load, in fact both PBP and DAP-92 cartridges, when fired, develop extra pressures, like, to say, +P+ or even +P++. That's why the PBP and DAP-92 cartridges can be fired only with .9x19mmm-chambered firearms which have been specifically engineered for them, while those firearms can normally handle any military-grade or commercial 9mm-Luger ammo).