The Resurgence of the FN 5.7x28mm

When it first debuted 30 years ago, the 5.7x28mm round was a bit of an oddity that flew under the radar. This .22-caliber bottleneck round more closely resembles a squat 5.56mm that bridges the gap between a rifle and pistol cartridge. In time, it became a niche caliber not unlike 41 Magnum, 10mm, or .357 SIG that have always seemed to hang on. Yet, for a myriad of reasons, the 5.7x28mm is on its way to becoming more of a mainstream pistol round as opposed to a PDW (Personal Defense Weapon) oddity. 

HISTORY OF THE 5.7x28mm

In the late 1980s, as the Cold War was winding down, NATO was on a quest to find a replacement for the Heckler & Koch MP5 submachine gun and the 9mm round in which it was chambered. Fabrique Nationale Herstal (FNH or FN) took up the challenge and sought to develop both a high velocity round and a PDW from the ground up. 

The FN P90 would ultimately be the PDW developed, and it’s truly unlike any firearm ever developed previous. It was short, compact, superbly ergonomic, and ideal for its intended users: support personnel and special operations units who need something more powerful and armor-defeating than a standard handgun. One of the standout features was a 50-round magazine mounted parallel to the bore.

One of the trademarks of 5.7mm is the extended capacities available; a P90 magazine holds 50 rounds without being bulky. Ammunition selection is still limited, but available loadings have been expanding since NATO adoption.

One of the keys to the success of the P90 was its unique round, and subject of this article, the 5.7x28mm. Unlike most small arms rounds, the 5.7mm is unique in that it has no parent case. FN pulled out all the stops and started from scratch. They did the same with the projectile design and construction as well. 

A 28mm case length with a 35-degree shoulder and 5mm of neck length makes for a short cartridge ideal for use in a handgun or PDW. The original bullet had a polymer core to decrease projectile weight (23 grains) and aid in velocity for penetration. However, this projectile was changed out within three years, by 1993 with the SS190 round that weighed 31 grains, had a steel and aluminum core, and seated deeper in the case.

One of the latest new designs, the Kel-Tec P50 is chambered in 5.7 and even eats from FN P90 magazines.

5.7x28mm BALLISTICS

From the 10-inch barrel of a FN P90, the shooter can expect a muzzle velocity of 2,350 fps. Although the lightweight bullet tends to lose velocity quickly at great distance, the round is perfect for its applications within 200 yards.

The 31-grain SS190, in particular, has excelled at penetration tests across the board. The Canadian RCMP famously fired the rounds through a P90, and the rounds penetrated more than 10 inches of ballistic gelatin after penetrating Level II body armor. NATO has tested the SS190 round fired through the P90 as capable of penetrating NATO Crisat armor (Level IIIA) at 200 yards.

NATO liked it so much, in fact, that in February of 2021, they officially recognized and adopted the FN 5.7x28mm as a NATO standard. 

THE P90 AND FIVE SEVEN

The initial firearm chambered in 5.7 was the FN P90. If you think this was a radical design today, imagine how it appeared 30 years ago. By the time the P90 made its way into firearm books and magazines, the design was more than a few years old, and Americans were in the black years of gun ownership. The federal 1994 Assault Weapon Ban had us by the throat, and anything that looked like and had the characteristics of the P90 was banned from importation and sale. Had that been the only firearm offered in 5.7mm, the round may have died on the vine. That wasn’t to be.

In 1998, FN revealed a pistol chambered in 5.7x28mm called the Five seveN. This is a polymer-framed, delayed blowback striker-fired pistol. Standard magazine capacity is 20 rounds, but restricted capacity 10-round magazines and extended length 30-round magazines are available.

Initially, the pistol was restricted to law enforcement and military sales only. Mostly, this had to do with the nature of the ammunition being armor piercing. However, by 2004, ammunition was available without the steel penetrator tip, and the pistol was available to civilian shooters in the United States. This was quickly followed by a civilian semiautomatic only version of the P90 known as the PS90. The PS90 had a longer barrel assembly, which added to the firearm’s overall length, and with the sunsetting of the Assault Weapon Ban, allowed use of the original 50-round magazine.

The question became: Would these two firearms be enough to catapult the proprietary round into the mainstream? Through very convoluted circumstances, and after a long interim, they somehow did.

The Diamondback DBX57 is an incredibly fun PDW that accepts FN Five-seveN pistol magazines.

BEYOND FN

Originally, this new caliber sparked plenty of curiosity and was compared to 22 Magnum, 22 Hornet, and various other cartridges with similar velocities and projectile weights. These comparisons don’t really do any of these cartridges justice but can provide somewhat of a baseline when trying to explain common attributes.

One of the first non-FN firearms to utilize 5.7 was the AR-57. This outwardly resembled an AR-15 and took the P90 50-round magazine, which also mounted on top of the handguard like a mirror image of the P90. The empty cases ejected through the magazine well of the lower receiver. Unfortunately, the manufacturer has since ended production, but we’re hoping someone produces something similar.

Other AR manufacturers like CMMG Inc. and Diamondback Firearms (see RECOIL Issue 53 for a full review of the Diamondback DBX) have picked up the torch and are producing rifles, carbines, and pistols that rely on the FN Five seveN pistol magazines. This probably made more sense for bringing over shooters who already owned the pistol but didn’t quite feel comfortable with the P90’s look or manual of arms.

Ruger 57 was Ruger’s more-approachable answer to FN’s Five-SeveN pistol.

In another related field of endeavor, Strum, Ruger & Co began producing a pistol chambered in 5.7 simply called the Ruger 57 (see RECOIL Issue 48). It shares no commonality of parts or magazines with any previous offering, and retails for 50 to 75 percent of the cost of the FN pistol. Having field tested this pistol for quite a while, it’s a great design, and the lower cost has probably brought many new shooters into the world of the 5.7x28mm round.

The biggest mystery of this resurgence has to do with the ammunition. From its introduction to today, FN has been extremely tight lipped about loading data. Essentially every recipe for cooking up your own handloads is from data that has been reverse engineered. A handloader can buy reloading dies, bullets, primers, and cases, but the exact type of powder and weight isn’t available via FN.

Which leads to the next point: Much of the factory ammunition by FN, or Fiocchi under the American Eagle brand, was dismissed as too expensive by many shooters. 

Although $19 to $35 for 50 rounds pre-pandemic probably seems cheap by 2021 standards, current offerings can go as high as $70 a box in some locales. Other ammunition manufacturers have been slowly joining the fold, but, again, the ammunition crunch we’re still feeling a year later has many of these manufacturers making ammunition higher in demand such as 9mm and 5.56mm.

First introduced just under a decade after the P90, the FN Five-seveN features a flush-fit 20-round magazine — and there are aftermarket mags and extensions available for capacities of 30-plus rounds.

LOOSE ROUNDS

The domain of 5.7 has mostly been in semi-automatic pistols, PDWs, and carbines. We’ve yet to see a bolt-action or lever-action rifle in this caliber, but there’s at least one revolver. John MacDonald, a gunsmith for JRH Gunsmithing out of Nevada, recently built a Ruger Single Six into a five-shot 5.7 conversion complete with a threaded barrel. Accuracy is fine, and initial suppressor testing indicates that this revolver may replace the notion that the Nagant Revolver is the only revolver capable of being effectively suppressed. 

Shooters who have come to appreciate this round are a dedicated bunch. It’s superb for small game and varmint control at close ranges, and personal defense if you understand the limitations of the round. The fun factor is high, especially when used in conjunction with a suppressor. Most rimfire cans introduced after 2016 are capable of handling the pressures of the 5.7, but always check with the manufacturer in question. Both .30 caliber and 5.56 NATO silencers are more than adequate for suppressing the 5.7x28mm.

With NATO adoption of the caliber and a half-dozen new firearms designed around it, this pop bottle PDW round is probably here to stay. 

The FN PS90 is the semiautomatic, longer-barreled version of the gun that started it all, the FN P90. If you think the design looks unique today, imagine coming across one 30 years ago!

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