FN P90 The FN P90 is a submachine gun produced by the Belgian Fabrique Nationale de Herstal to replace the pistol - caliber submachineguns . Description . The submachine FN P - 90 has several features that go beyond its unconventional design . Actually the proposal of the FN Herstal launched this little gun when the market was to provide a self - defense weapon ( PDW concept Personeal Defense Weapon ) , compact enough to be carried by crew members with land and air vehicles , and had a power equivalent to fire an assault rifle at distances of 150 – 200 meters . In order to gather these requirements in a submachine , the FN had to develop not only a new weapon , but also a new caliber , bringing back the ammo - style " bottle " found in rifles , submachine to the compact . The new size is 5 . 7x28mm , which is very small , being slightly larger than 9mm ammunition , in terms of length , but with an initial speed at the muzzle of the P - 90 , which has 11 ½ inches , 850 m / sec . Speed equivalent to a rifle at 7 . 62x51mm . Given this aspect in all , still , the fact of being fully jacketed bullet , the result is a very effective performance piercing . Certainly , this penetrating ability , and the small diameter of the projectile stopping power of ammunition should not be very significant , because when there transfixed excessive , there will be little energy transfer to the target , thereby reducing stopping power . Still speaking in the ballistic characteristics of this new ammunition , the trajectory of the bullet is extremely tense , and after 300 meters , the drop of the trajectory of the bullet is extremely sharp . The FN has chosen BullPup configuration to achieve to make its new compact weapon . In this configuration the gun mechanism is mounted within the stock optimizing the internal space of the gun , and limiting the length of the P - 90 in a mere 50 cm . The operating system is the blowback with the bolt closed , feature , such that decreases the problems of using the P - 90 in terms of dirt or merging . The finish of the P - 90 is in high - impact plastic , and the barrel and firing mechanism , the only metal parts being the P - 90 a very light gun . Other notable advance in the P - 90 is its reflex sighting system which is already standard . With this aim , the soldier has an electronic point that is projected on the lens of sight , making it easier to target even in low visibility conditions . Actually there is a way of night sights , specifically , available on target system and allows the use of P - 90 normally under these conditions . New versions of the P - 90 , as the P - 90 TR ( Triple Rail ) , show that the FN has not stopped thinking about how to improve your project by placing picatini rails on top and sides of the P - 90 , facilitating the mounting of accessories as laser sights and flashlights into the gun . For the civilian market North America and Europe , there is a carbine version known as PS - 90 , and whose pipe is larger , with 16 inches in length and only semi - automatic operation . With the P - 90 , FN is a high - tech and high reliability with a single direct competitor in the market that is the modern HK MP - 7 Variants . The " P90 TR " ( Triple Rail ) variant was introduced in 1999 . It features a receiver - mounted triple MIL - STD - 1913 rail interface system , or " Triple Rail " . Originally , there was one full - length rail on the top of the base and two rail stumps on the sides of a slightly redesigned upper receiver . This original version was phased out , and is no longer in production . The newer " TR " models , initially introduced as " TAC " ( for ' tactical ' ) use the standard upper receiver , but with a full - length rail in place of the standard sight . The top rail itself has emergency iron sights contained just under the mounting area . In both cases of the " TR " , the side rails serve to mount accessories such as laser aiming devices or flashlights , while the integrated top rail will accept various optics with no tools or additional mounting hardware required . The " P90 USG " ( United States Government ) variant is similar to the standard P90 with the exception of a revised optic system , developed based on input from the United States Secret Service and other government agencies . The aluminium sight uses a non - magnified black reticle that does not require ambient light . The " P90 LV " ( Laser Visible ) and " P90 LIR " ( Laser Infrared ) models add an integrated visible laser sight or infrared sight , respectively . They were introduced in late 1995 . Both units are manufactured by the Australian company Laserex Technologies . The laser ' s power switch is a green button located under the trigger grip . The lasers have three internal settings : " off " – to prevent accidental activation , " low - intensity " – for combat training and extended battery life , and " high - intensity " – for maximum visibility .