The P90 is a Belgian designed submachine gun. The weapon’s name is an abbreviation of Project 90, which specifies a weapon system of the 1990s. The P90 is considered a Personal Defense Weapon (PDW), and was designed as a compact but powerful firearm for vehicle drivers, operators of crew-served weapons, support personnel, special forces and anti-terrorist units. Developed between 1986–1987 at Fabrique Nationale de Herstal, the P90 features a compact bullpup design, ambidextrous grip and a polymer and alloy-based construction. The weapon contains several innovative features including the proprietary 5.7x28mm ammunition, designed for greater penetration of body armour than pistol ammunition. The P90 and variants are in use by military and police forces in over thirty countries worldwide, and sports models are popular among civilian shooters.

 

The P90 is a selective fire straight blowback-operated weapon with a short recoiling barrel and fires from a closed bolt. The return mechanism consists of two parallel spring guide rods that also guide the bolt carrier assembly. The weapon uses an internal hammer striking mechanism and a trigger mechanism with a three-position rotary dial fire control selector, located centrally beneath the trigger. The fire selector also provides a manual safety against accidental firing. The dial in the "S" position – weapon safe, "1" – semi-automatic fire, "A" – fully automatic fire.

 

When set on "A", the selector provides a two-stage trigger operation. Pulling the trigger back slightly produces semi-automatic fire and pulling the trigger fully to the rear will produce fully automatic fire. The "safe" setting disables the trigger. The P90 uses an original horizontally-mounted feeding system that is patent protected in the United States (U.S. Patent 4,905,394 dated March 6 1990), authored by René Predazzer. It uses a 50-round box magazine, mounted parallel to the bore axis that locks in place between the charging handles and optical sight, flush with the receiver top cover. The magazine is made of a lightweight, translucent polycarbonate and allows for visual ammunition verification. The base of the magazine is located near the muzzle end, the feed lips above the barrel chamber in a circular bulge that contains the feed tray.

 

Cartridges in the magazine body are double stacked to the left side. The magazine features a follower with rollers and a spiral feed ramp that will rotate a cartridge 90° to the right aligning it in a double stack pattern within the magazine. The weapon’s hammer-forged steel barrel is fitted with a ported, diagonally cut flash suppressor that also acts as a recoil compensator. Early models did not have the cut in the flash hider. The P90 is equipped with an unmagnified HC-14-62 reflex sight from Ring Sights, which enables quick target acquisition up to 150 metres (490 ft) and operation in low-level lighting conditions thanks to a tritium-illuminated aiming reticle. Newer units are fitted with the Ring Sights MC-10-80 sight designed specifically for the P90. It uses a forward-aimed fiber optic collector to illuminate the daytime reticle, which consists of a large circle of about 180 Minute of arc (MOA), with a 20 MOA circle surrounding a dot in the center. The night reticle consists of an open "T" that is primarily illuminated by a tritium module or moonlight and ambient light drawn in by an upward-facing collector.

 

The sight is adjustable for both windage and elevation and can be used with night vision equipment. Auxiliary fixed sights are provided on both sides of the receiver's cast aluminium optical sight housing. The P90 is fully ambidextrous; it can be operated by right or left-handed shooters without making any modifications to the weapon. The charging handle, auxiliary fixed sights and magazine release are symmetrically distributed on both sides of the firearm. The manual fire selector below the trigger can be operated from either side. Spent cartridge casings are ejected downward through a chute located aft of the pistol grip, keeping fired cases out of the shooter's line of sight. The P90 is designed in the bullpup configuration which reduces the firearm's overall length while retaining a full-length barrel. The pistol grip with thumbhole and oversized trigger guard act as the forward grip, a handstop is incorporated into the weapon's stock to prevent the operator from accidentally reaching out in front of the barrel during firing.

 

The P90 is a modular firearm and consists of 69 parts that disassemble into four main groups: the barrel with integrated sight assembly, receiver with return mechanism, stock body with trigger and firing mechanism and the magazine. The P90 makes extensive use of polymers and lightweight alloys to reduce both the weight and the cost of the weapon. It can also be fitted with a laser aiming module integrated into the stock body, beneath the barrel and the SP90 suppressor, made by Gemtech, which has a length of 184 mm (7.2 in) and weighs 550 g (19 oz).