The FN P90 is one of the most visually distinctive firearms in modern history, and the question "what caliber is a p90" is almost always the first topic of discussion for anyone encountering it for the first time. This personal defense weapon (PDW) utilizes the 5.7×28mm cartridge, a round specifically engineered to penetrate body armor while maintaining controllability in full-auto fire. Understanding this specific caliber is essential to grasping why the P90 revolutionized tactical shooting and remains a benchmark for compact, high-performance firearms decades after its introduction.
The 5.7×28mm Cartridge: Origins and Design Philosophy
The heart of the P90 is the 5.7×28mm round, developed by FN Herstal in the late 1990s. Unlike traditional pistol cartridges, the 5.7×28mm is a bottleneck cartridge designed for rifles, but scaled down for compact use. It was created with a specific military purpose: to offer soldiers and law enforcement officers a weapon capable of defeating Level IIIA body armor at typical close-quarters engagement distances. The cartridge features a small, lightweight 40-grain projectile that exits the barrel at extremely high velocities, exceeding 2,300 feet per second, which contributes to its famous flat trajectory and low recoil impulse.
Ballistics and Performance Characteristics
When discussing what caliber is a p90, you must examine the performance metrics that define the 5.7×28mm. The round is capable of penetrating multiple layers of Kevlar and standard steel barriers that would stop larger, slower pistol rounds like 9mm Luger. This deep penetration is achieved without the heavy recoil associated with rifle rounds like 5.56 NATO, making it ideal for close-quarters battle where rapid follow-up shots are critical. The flat trajectory ensures that the point of aim closely matches the point of impact out to 100 meters, a significant advantage over traditional handgun cartridges.
Muzzle Velocity: Approximately 2,332 feet per second.
Effective Range: Point target engagement up to 200 meters.
Magazine Capacity: Standard 20-round box magazine, with extended options available.
Recoil Management: Significantly lower than rifle rounds, aiding in rapid target acquisition.
Why the Caliber Defines the P90's Role
The selection of the 5.7×28mm dictates the tactical application of the P90. Because the cartridge offers a blend of penetration and controllability, the weapon is classified as a Personal Defense Weapon rather than a standard submachine gun. This classification means the P90 bridges the gap between a pistol and a rifle, offering the stopping power necessary for military engagements while remaining lightweight enough for vehicle operators or security personnel to use effectively all day. The caliber ensures the weapon is not over-powered for urban environments but is still formidable against threats wearing protective gear.
Ergonomics and Handling
Another reason the question "what caliber is a p90" is so prevalent is due to the weapon's unique design. The compact size of the 5.7×28mm round allows the P90 to feature a remarkably short barrel and overall length, making it highly maneuverable in tight spaces. The weapon’s distinctive bullpup layout places the action and magazine behind the trigger, resulting in a full-sized rifle barrel in a package roughly the size of a standard pistol. This design, combined with the ergonomic vertical foregrip, allows for rapid target transitions and exceptional control during rapid fire, whether the user is standing, kneeling, or moving from cover to cover.
