The 5.7x28mm is a small-caliber, high-velocity, centerfire cartridge resembling a miniature rifle round. This type of ammunition was the first of its kind, designed for the Personal Defense Weapon (PDW), a new class of firearms that are neither rifles nor submachine guns.
Before the PDW: The Submachine Gun
Until the end of the Cold War, one of the most effective infantry weapons for close-quarters combat was the submachine gun (SMG). These weapons are compact, relatively lightweight, fully automatic, and cause less recoil than rifles and machine guns.
However, as technology progressed, ballistic body armor made of materials such as Kevlar became more commonplace. Although such armor provides little to no protection against traditional rifles, they were efficient at stopping handgun ammunition, from .22 Long Rifle to .44 Magnum. A conventional 9x19mm submachine gun, such as the Uzi or the H&K MP5, could not penetrate Kevlar body armor.
SMGs of the time simply could not be relied upon to stop threats wearing body armor, yet arming all personnel with rifles was not feasible either due to their weight and length. It became clear that a new category of weapon was needed, one with the penetration capabilities of the rifle and the compactness of the submachine gun. It was these needs that created the idea of a Personal Defense Weapon.
In the late 1980s, FN Herstal responded to NATO’s requests for a potential replacement of the 9x19mm cartridge and all associated weapons. The specifications included a new cartridge, a shoulder-fired weapon, and a handgun.
The new weapons had to be lightweight, high capacity, and compact enough to carry comfortably even in a cramped cockpit. The new cartridge had to be able to penetrate all soft body armor commonly available at the time while having more range, accuracy, and terminal effectiveness than 9x19mm.
The 5.7x28mm FN cartridge
The 5.7x28mm FN cartridge uses a 28.9mm Boxer-primed brass case, tipped with a .224” bullet - the same diameter as 5.56x45mm and .223 Remington, but shorter in length.
The standard military 5.7x28mm cartridge is known as the SS190. This ammunition type uses a 31-grain aluminum-core bullet with a steel penetrator. When fired from the P90, the SS190 achieves a muzzle velocity of 2,350 feet per second and can penetrate any armor equivalent to NATO CRISAT specifications at up to 200 meters.
Other projectile types were later developed, intended primarily for training and civilian use. The SS192 hollow-point, SS195LF lead-free FMJ, and the SS196SR sporting round with Hornady V-Max bullet are all legal to possess in the United States.
As time passed and 5.7x28 gained acceptance with US civilian shooters, other major ammunition manufacturers, such as Federal and Speer, started offering 5.7x28 ammo of their own.
The First PDW: The FN P90
FN Herstal introduced the FN P90 as a shoulder-fired weapon system. The weapon first saw service in 1991 when Belgian special forces used it in the Gulf War. Since then, more than 40 countries have adopted it.
The P90 was ahead of its time. Making extensive use of polymers, the P90 is a bullpup firearm with a unique feeding system, employing a 50-round magazine sitting on top of the receiver.
The cleverly-engineered magazine stacks the rounds perpendicular to the barrel until reaching the end, where a spiral-shaped feeding ramp rotates the cartridges, bringing them to the feed lips. When fired, the spent cases eject from the bottom.
The P90 is a fully ambidextrous system. Besides the top-loading magazine and bottom-ejecting cases, it also features an ambidextrous charging handle and fire selector, capable of either semi-automatic or fully-automatic fire, with an average cyclic rate of about 900 RPM.
The original version of the P90 featured an integrated red dot sight, but later versions replaced it with a short length of Picatinny rails.
A civilian version, known as the PS90, was later introduced. This model is semi-automatic only and uses a 16” barrel for compliance with the National Firearms Act, and is available for purchase on the US civilian market.
Due to its unique and futuristic design, the P90 also gained wide popularity in countless fictional media, including movies (The World is Not Enough), TV shows (Stargate: SG-1), and video games (Counter-Strike, Battlefield).
First introduced in 1998, the Five-Seven was designed as the handgun companion to the P90.
The Five-Seven is a full-size, polymer-framed pistol. It uses a steel slide encased in a polymer shell, a concealed hammer, an ambidextrous manual safety, and an accessory rail. Most importantly, it has a double-stack, high-capacity magazine capable of holding 20 rounds. Even when fully loaded, the Five-Seven remains very light, at just 1.6 lbs.
Although the shorter barrel naturally results in a shorter effective range and a lower muzzle velocity, the SS190 projectile still has a velocity of 2,130 feet per second out of the Five-Seven. It remains capable of defeating NATO CRISAT body armor at up to 100 meters, well beyond the typical engagement distance for a handgun.
Other 5.7mm Firearms
Initially, only FN Herstal offered firearms that could shoot 5.7x28mm, and although high-quality, the PS90 and Five-Seven come with a hefty price tag.
To help make 5.7x28 more accessible, various US gun makers introduced designs of their own, often using P90 and Five-Seven magazines, such as the AR-57 or the CMMG Banshee.
In 2012, Excel Arms was the first US gun maker to introduce a completely original 5.7mm firearm, the Accelerator MP-57. However, it remained relatively obscure.
The state of 5.7x28mm in the US civilian market largely remained stagnant until 2019, when Ruger unveiled the Ruger-57.
Intended to be an affordable competitor to the Five-Seven, the Ruger-57 offers many of the same features, including ambidextrous controls, a polymer frame, and a 20-round magazine, but with an MSRP of less than half that of the Belgian product.
Reviewers praised its reliability and accuracy, believing it would help make the 5.7x28mm cartridge more popular and approachable in America.
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