FN P90

  
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.

SMG vs. PDW

The 9mm cartridge has been around for over a century as the gold standard for pistols and submachine guns, offering respectable power for a case of its size. Unfortunately, with the advent of lightweight body armor, the old Parabellum just doesn't cut it situations where the enemy might be wearing kevlar; 9mm ammo is so ubiquitous that Class II body armor is specifically defined as being "9mm FMJ-proof." PDWs (personal defense weapons) are a recent designation for pistols and SMG's built to compromise lighter forms of body armor, an effect generally achieved by using newer and more advanced bullet designs. In the case of the P90 (and its sister pistol, the Five-seveN), FN Herstal developed the 5.7x28mm SS190 cartridge. As of 2009, no other company has adopted the cartridge.
  
     

"Hot .22"

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 sited the bullet's measly 32 grain weight (compared with the 9mm's 115-140 grains or the .45 ACP's 165-200) as being 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.
 
Though studies have mostly debunked this assumption, this public hazing of the smaller FN round has influenced the way game developers use the P90 in their 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. To be fair, this drawback is probably common to keep the P90 from being overpowered, as it already sports a 50-round magazine (compared to the 32-rounders most SMG's carry) and is assembled from expensive, high-quality parts.