The P90 is an automatic "personal defense weapon" (the first weapon of the type ever produced) that fires the 5.7x28mm FN armor-piercing round. Built for use by support personnel and vehicle operators, the P90 and its variants have become a staple of counter-terrorist and high-level police units for its size and firepower. It is fully ambidextrous and can be disassembled without tools for ease of maintenance.
The translucent magazine the P90 uses is loaded on top of the gun for easy mag reading, and the shells are ejected out the bottom for ambidexterity. The P90's bullpup design accommodates the larger magazine and significantly improves the system's accuracy, with the drawback that the bullets must be rotated 90 degrees from the magazine to the firing position. It is nearly always fitted with the Ring Sights MC-10-80 reflex sight, designed specifically for this weapon system.
The size of the 5.7 FN round has stirred up controversy over its stopping power since the bullet was first unveiled. The 5.7 was the first pistol round touted as an armor-piercer to achieve commercial success, but many have claimed the bullet's measly 32 grain weight (compared with the 9mm's 115-140 grains or the .45 ACP's 165-200) is insufficient to kill on impact. This has earned the 5.7, along with H&K's 4.6x30mm AP round, the pejorative label of a "hot .22", referring to the .22 long rifle round normally used for target shooting.
Although studies have discredited this perception, it has influenced the way developers implement the P90 in games; when compared with other submachine guns in games such as Call of Duty 4 or the Rainbow Six series, the P90 almost always has the lowest damage rating. However, this is ultimately necessary to keep the weapon from being overpowered, as it already sports a 50-round magazine as opposed to the 32-rounders most SMGs carry.