“This is really neat! What’s it good for?” The most typical reaction to the AR-57 upper has been that of amusement. Take a blowback AR-15 upper, mate it with an FN P90 magazine and you get this very curious contraption bridging the gap between .22 Magnum carbines and .223 AR-15 rifles.
Contrary to the oft-posted claim, 5.7×28 isn’t quite identical to .22 WMR in ballistic performance. Comparing 40-grain loads, CCI Mini Mags and American Eagle TMJ, we get similar initial velocity but dissimilar trajectory. At 1,950 fps from a rifle, .22 WMR load drops to transonic velocity around 200 yards. Only a little quicker out of the bore at 2,020 fps, the 5.7 bullet remains above speed of sound out to nearly 350 yards thanks to its much superior ballistic coefficient. Terminal effects also differ, with pointed 5.7 bullets tumbling more readily. Being centerfire, 5.7×28 cartridges are rather less delicate in handling. Being bottlenecked, they also extract easier at the cost of reduced box magazine capacity. Larger FN57 magazines hold 20 rounds while Kel-Tec PMR-30’s smaller magazine holds 30. At the same time, loading FN magazines is faster and easier. .22 WMR ammunition is about half the cost of 5.7×28, and the upcoming Kel-Tec CMR-30 carbine is also about half the weight of the AR-57 rifle. So the gains over .22 Magnum are mainly in reliability, range and slight increase in terminal effect. And, of course, in capacity; P90 magazines hold 50 rounds each, making it unnecessary to carry spares when riding around a farm.
On the other side of the power spectrum, 5.7 isn’t even close to AR-15’s standard .223 Remington. The only similarity is the identical bullet caliber 0.224-inch 40 grain .223 loads range in velocity from 3,650 to 3,800—over three times the kinetic energy. Even though the second generation AR-57 upper uses a thinner fluted barrel to drop a pound, it is still similar to the more powerful rifle in weight and dimensions. The efficiency of .223 ammunition is also greater, with bullet weight ranging from 40 to 77 grains instead of 27 to 40. At .50 cents per round delivered, 5.7 costs less than specialty ammunition but more than .223 ball.
So what does AR-57 have going for it? Quite a lot, actually. With the top-mounted magazine, it ejects down: left and right-handed shooters can shoot it comfortably, though the non-reciprocating charging handle on the right is easier for southpaws to reach. Spent casings collect in a neat pile under the gun. Quite a few shooters use an old magazine with spring, follower and feed lips removed as an improvised brass collector. The muzzle rise and recoil are non-existent, the muzzle blast is mild and relatively small and light. You can use 5.7/.22 Mag-rated sound suppressors instead of the larger 5.56 cans. Suppressed, the AR-57 has no gas blowback towards the shooter, unlike almost every conventional AR-15. The second-generation forend is heavily skeletonized for weight reduction and air flow. I covered up some of the ridges with Ergo grip panels to provide non-abrasive support surfaces, but even with that, the barrel never got hot. It helps that 5.7×28 burns one-fifth as much powder as .223, generating less heat and far less muzzle blast. For firing prone or benched, the top-mounted magazine is also more comfortable than even the shortest box magazine protruding from the bottom.
Attaching the magazine is quick and simple; you can make the change without losing sight of the target. Translucent polymer magazines give a visual indication of the remaining ammunition level, which is handy because the rifle lacks last shot hold open. The magazine latch changed from the previous generation and now pivots around the center axis. Pivoting it front or back from either side releases the latch.
To reduce the overall weight, I used a GWACS polymer lower. Contrary to the apprehensions of my range mates, ejecting empties left no traces on the inside of the magazine well, and the upper and lower mated smoothly. Between the lighter barrel and the GWACS lower, I dropped two pounds off the rifle compared to the first generation guns. The top-mounted magazine requires the use of relatively short optics: I opted for the Primary Arms 2.5 power prismatic with illuminated BDC reticle. While the drop calibration is for .223, the rangefinding hashes work the same, and you can calculate or determine the drop empirically. Instead of zeroing at 50 yards, as recommended, I zeroed at 100. The optic manual assumed 50-300 point-blank range based on a human-sized foe, but my targets were a good deal smaller. The nominal 400-yard drop mark was on for 150, and 500/600 would be pro-rated accordingly. 2.5x is quite good out to 200 yards on point targets, while the 4x variant would have been preferable for varminting further out to the maximum effective range of the cartridge. My purpose from the start was to make this carbine suitable for defense as well as for hunting, so lower magnification was the way to go.
Even a 2.5x scope can be a hindrance up close, so Dueck Defense offset sights were added on the right. A right-handed shooter would rotate the rifle 45 degrees counter-clockwise, while a left-handed shooter would just shoot with the right eye with the rifle remaining upright. Set to the large aperture, the sights provide a close-range alternative as well as an emergency backup. Since iron sights can be lacking in very low light, I added a Viridian C5L light and green laser combination to the very front to minimize the occlusion of the light beam by the barrel. With it, foes or varmints can be positively identified and targeted even at night.
For the range test, I had 150 rounds of American Eagle 40 grain TMJ ammunition. I selected this load because most of the FN ammunition is frangible or rapidly expanding, more effective on small and medium game than on hominids or vehicles. Thickly jacketed Federal bullet is the one commonly available load that would work better for defense, in my opinion. While its velocity is listed as 1,655 fps referring to performance from a pistol rather than a rifle. All 150 rounds cycled and fired flawlessly. No muzzle flash was observed. Using 2.5x scope and a bag for support, we found real-life accuracy to be just under 3MOA. Using a lead sled and a high power scope would have reduced the group size, but my interest was in learning how it would perform if fired under field conditions. Reading a FN57 forum discussion, I recall notes of 1MOA achieved with handloads and careful bench-resting of the test gun.
All six-shooters, including a diminutive teenage girl, found the rifle very comfortable and controllable in rapid-fire. Compared to P90, AR-57 can have either a better trigger (AR Mil-Spec) or a much better trigger (such as a Geissele or a Timney), giving an edge in practical accuracy. The form factor and manual of arms differences are a matter of personal preference.
As a defensive tool, the AR-57 is a niche item, geared to users who would find lower recoil and higher magazine capacity a plus. While 40/60/100 rounds .223 magazines are available, they protrude a good deal and add much weight. The same is true of the drums, plus a hefty price tag compared to the less than $11 charged for an AR-57 magazine. Low recoil allows for very rapid fire, so the lower velocity of each bullet than with .223 can be compensated by more lead on target in the same time. As an entertaining plinker, it’s among the best. A small sports car may be less economical than an econobox and less capable than a truck, however, people buy them for the handling and the fun factor. The same is true of the AR-57.
Tell us what you think about the AR-57 in the comment section.