The AR57 Could Be the Weirdest AR Variant You’ll Ever See

AR57 photographed during a coup attempt in Venezuela.

What happens when you cross an AR15 with an FN P90? You get arguably one of the weirdest variations of firearm to have ever come out of Stoner’s ages-old platform — the AR57 (AR Five Seven)…an AR for 5.7×28 ammo.

The AR57

Chambered for 5.7×28 Ammunition

Ian D’Costa

Originally, the 5.7×28 mm cartridge the latter half of the AR57 name refers to was developed in the 1990s as part of a NATO plan to replace 9×19 mm as the new standard sidearm round with all NATO members.

The plan revolved around the primary requirement to build a cartridge that could be used with personal defense weapons as well as pistols. It had to demonstrate better performance metrics and terminal ballistics than the 9mm cartridge and needed to be armor-piercing.

FN Herstal developed the 5.7×28 mm cartridge as a result, paired with its P90 PDW and later the Five-seveN pistol. NATO’s plan went absolutely nowhere, and FN was forced to look elsewhere (including the commercial market) to find buyers for its futuristic cartridges and guns.

The AR57 is an AR15 profile rifle chambered in 5.7x28mm. Many versions will accept a standard FN P90 magazine, though it's possible there are some that take a proprietary mag.  Image via Wikipedia.
The AR57 is an AR15 profile rifle chambered in 5.7x28mm. Many versions will accept a standard FN P90 magazine, though it’s possible there are some that take a proprietary mag.  Image via Wikipedia.

For years, FN’s Five-seveN and its semiautomatic PS90 dominated the 5.7 mm gun arena, but in 2008, the AR-57 popped out of nowhere, an alternative to the PS90, albeit with the AR layout so many gun owners find familiar.

However, while the AR57 bears a resemblance in passing, it’s anything but an AR-15.

AR 57: Unusual Features

For starters, it uses PS90 top-loaded 50-round mags, which hold rounds perpendicular to the barrel. They’re then swiveled into the forward-facing position to line up with the chamber.

A P90/PS90 mag showing the unique perpendicular feed (Photo Wikimedia Commons by ROG5728)

The AR-57 sacrifices some of that AR customizability we’ve all come to know and love by making use of a monolithic upper with the barrel threaded directly into the upper. Instead of a gas-tube operating system, the gun uses straight blowback to cycle rounds and ejects spent casings through the mag well of the lower.

Early versions of the AR57 featured a non-reciprocating charging handle on the right side of the upper and a 3, 6, and 9 o’clock Pic rail on the handguard, with a small 12 o’clock rail for a front sight or red dot. Eventually, an upper with an MLOK handguard and an ambidextrous charging handle came to fruition as an alternative.

AR57 LLC, the company that produced the weapon, offered buyers two options: a complete upper that could be mated to any AR-15 lower and work with most mil-spec fire control groups or a complete gun.

Diagrams and explanation from an AR 57 patent.

Semiautomatic Rifle with Downward Ejection

From Patent No. US20110168009

Abstract: A bolt assembly for a rifle is configured for recoil blowback operation and cooperation with a round of ammunition dispensed from a magazine into a firing chamber of the rifle. An extractor disposed in a lower, forward portion of the assembly and an ejector disposed in an upper, forward portion of the assembly further cooperate with the round of ammunition to extract a spent cartridge of the round of ammunition from the firing chamber and eject the spent cartridge downward from the firing chamber. 

In brief, the modification replaces the upper receiver, barrel, bolt assembly, and mag of the standard AR-15 with a conversion adapter called an AR-57 in which a new rifle barrel and a modified assembly are installed. More importantly, the AR-57 upper is configured to receive a standard longitudinal mag along the top portion of the AR-57. The result is a more compact, well balanced, and more maneuverable semiautomatic rifle that improves recoil performance and ejects spent cartridges downward instead of sideways. The top-mounted, longitudinal mag employed for illustration purposes herein is a standard type manufactured by Fabrique Nationale de Herstal of Belgium.

FIG. 1 illustrates a prior art semiautomatic rifle of the AR-15/M16 type;FIG. 2 illustrates one embodiment of a semiautomatic rifle modified according to the present invention; FIG. 7 illustrates an exploded view of an alternative embodiment of an upper receiver and bolt assembly for an AR-15 type semiautomatic rifle according to the present invention;

So, What Exactly Was the Point of the AR 57?

It’s hard to say.

The AR-57 was loosely marketed as a PDW, retailing with 12- and 16-inch barrel options . Firepower certainly wasn’t the issue (though that might depend on how you define firepower. With absurdly light recoil and a high-velocity round, the AR-57 was guaranteed to pack a decent punch at closer ranges. And with ridiculously low felt recoil, 5.7x28mm is very easy to shoot. No need for a muzzle brake here! 

By 2017, the AR-57 began its fade into the ether, and today, not much exists to suggest that it was ever commercially successful, though complete guns, as well as the monolithic uppers, still pop up from time to time. This lack of broad after-market support is at least part of the reason it’s so difficult to obtain replacement parts like an AR57 bolt carrier group; happily, many standard AR15 parts do fit and are readily available.  

It stands to reason that the top-loaded mag would’ve also contributed to the gun’s popularity demise. Perhaps the biggest nail in the coffin was that the AR-57 was too early for the market, hitting shelves at a time when 5.7 mm rounds were just too niche for most consumers.

The CMMG Banshee 100 Mk4 is one of a few PDW options in 5.7 mm available today (Photo CMMG)
The CMMG Banshee 100 Mk4 is one of a few PDW options in 5.7 mm available today (Photo CMMG)

Today with the advent of the Ruger-57 , and CMMG releasing a variety of PDW options chambered for that caliber, 5.7 mm is slowly clawing its way out of obscurity. Maybe the AR-57, if released today, would find a much more receptive and tolerant audience, but alas, it just wasn’t meant to be.

Snapshots of the movement of a round of ammunition from the longitudinal mag into the firing chamber before extraction. 

FIG. 6A illustrates a side elevation of a portion of the section of FIG. 5 surrounding the firing chamber, showing a fresh round of ammunition entering the firing chamber; FIG. 6B illustrates a side elevation of a portion of the section of FIG. 5 surrounding the firing chamber, showing the fresh round of ammunition in position for firing;

(via Google Patents)

Oddly enough, the AR-57 has somehow made its way to Venezuela, where it was photographed during a recent attempted coup.

An FN P90 style magazine (i.e., longitudinal) atop an AR57 in Venezuela.
An FN P90 style magazine (i.e., longitudinal) atop an AR57 in Venezuela. We don’t currently have one of these at the Rainier Arms OKC gun store; they’re damn rare. But we’ll make an announcement on social media so you’ll know to come in and, you know, finger it.
Close-up of top-feeding AR 57 during unrest in Venezuela.
Close-up of top-feeding AR 57 during unrest in Venezuela.

Learn more about the AR 57

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