Ruger AR-556 Review

March 17, 2015 By Joel J Hutchcroft

When Ruger announced about five years ago that it was making an AR-style rifle, the gun world went wild. That first AR-platform rifle from Ruger (called the SR-556) was a big hit, but because it was a piston gun with a retail price tag of around $2,000, plenty of shooters were reluctant to buy one. Well, now Ruger has brought out a direct impingement AR, and the MSRP is a very reasonable $749. I'll bet a lot of those guys will be ponying up their hard-earned cash for the new Ruger AR-556.

The Gas System

Obviously, the fact that Ruger is offering a direct impingement AR is big news. When the company brought out its piston-driven AR, every gun writer who thought it was a good thing wrote about the advantages of the piston system, saying things like piston systems tend to be cleaner shooting. They pointed out that with the direct impingement system unburned powder and gases are vented back into the rifle's action, which causes a lot of fouling, sends noxious gases back toward the shooter, and makes the action very hot. With the typical piston-driven system, those hot gases and unburned powder are vented out through the front of the gun.

A lot of AR aficionados think the direct impingement system is just fine. In fact, they would argue that with the direct impingement system parts tend to last quite a bit longer, as long as the gun is properly cleaned at regular intervals. They would also say that the most accurate ARs have always been direct impingement guns. And they could easily contend that direct impingement guns have softer recoil impulses, tend to be lighter in weight, and generally cost less.

I'm not taking a side in the debate. I'm merely pointing out that there are good arguments for both systems. Either way, Ruger now has ARs with both mechanisms.

The new AR-556's gas system is a mid-length system, in keeping with its carbine-length barrel (more about the barrel in moment). The milled gas block is described as an A2, F-height block. It's pinned in place, and it has multiple sling-attachment points and a bayonet lug.

The AR-556's lower receiver is a 7075-T6 aluminum forging. Its finish is Type III hard coat anodized. The trigger guard opening is enlarged.

The flat-top upper receiver is also 7075-T6 aluminum. It has the typical forward assist, dustcover, and brass deflector. The slotted top rail measures 5.5 inches long. And like the lower, the upper receiver wears a Type III hard coat anodized finish.

The bolt is 9310 alloy steel. The bolt carrier group has a staked gas key, a chrome-plated bolt carrier inside diameter, and a chrome-plated gas key inside diameter. External finish is matte black oxide.

The Barrel

The AR-556's medium-contour barrel is a cold hammer-forged 4140 chrome-moly steel tube with a 5.56 NATO chamber and M4 feedramp cuts. The barrel's diameter is 0.85 inch under the handguard, 0.75 inch under the gas block, and 0.70 inch forward of the gas block. The length is 16.1 inches, and the twist rate is 1:8.

That's going to please a lot of AR shooters because a twist of one turn in 8 inches will stabilize bullets across a wide range of weights. Everything from 35 to 77 grains should shoot pretty well in the 1:8 twist rate. Only the heaviest bullets for this caliber (e.g., 90 grains) probably will not stabilize.

The two-piece handguard is constructed of heat-resistant glass-filled nylon in the traditional round shape. The barrel nut and delta ring are a new patent-pending design that accepts standard carbine-length handguards and uses a standard wrench. It can be swapped out for a mil-spec nut if the owner so desires.

The Trigger

The trigger on ST's sample AR-556 was good. Ruger has taken some heat in the recent past for the quality of its triggers. Complaints have centered around the triggers being excessively heavy and with lots of creep. The single-stage trigger on the AR-556 I fired for this report was pretty good. Pull weight is a little heavier than I prefer, but it was consistent. It averaged 7 pounds, 8 ounces over 10 measurements. Those values varied 12 ounces across all of those measurements.

The Sights

The AR-556 comes with sights. The rear is Ruger's own Rapid Deploy folding sight that's adjustable for windage. It has a peep-type aperture and side protection ears. The front post sight is the classic A2 style, and it's adjustable for elevation.

Shooting Results

For putting the AR-556 to a shooting test, I picked seven .223 factory loads from six manufacturers, including Australian Outback, Black Hills, Federal, Hornady, Remington, and Winchester, with bullets ranging in weight from 52 grains to 69 grains. The details are listed in the accompanying chart. Overall, the AR-556 averaged 1.79 inches for five-shot groups at 100 yards. Its three-shot overall group average was 0.94 inch. I removed the rear sight and mounted my trusty Nikon M-223 AR 1.5-6X 24mm scope with illuminated reticle in a Nikon one-piece mount for the accuracy shooting session.

Top velocities in the AR-556 came with Black Hills's 52-grain ammo and Hornady's 55-grain TAP load, averaging 2,853 fps and 2,867 fps respectively. No surprises there. What did surprise me, however, was that the most accurate bullet weight was 55 grains. I fired three different brands of 55-grain ammo, and those three loadings averaged 1.55 inches. The most accurate load (Winchester's Ballistic Silvertip) averaged 1.38 inches.

According to Ruger spokesmen, the AR-556 was extensively tested during its development, with over a quarter-million rounds expended during the final validation, endurance, and jury testing. My short time with the new direct impingement carbine, shooting more than 500 rounds for accuracy and function in one afternoon, confirms that Ruger did its due diligence with this gun. I didn't have a single malfunction, accuracy with all bullet weights I fired (from 52 to 69 grains) was very good, and trigger pull was decent. And you sure can't beat its very reasonable MSRP.

The new AR-556 features a 16.1-inch barrel with a 1:8-inch rifling twist rate, a six-position collapsible M4-style buttstock, an ergonomic pistol grip, and a glass-filled nylon handguard. It's the first model to be built at Ruger's new factory in Mayodan, North Carolina.

The new AR-556 carbine's bolt is made of 9310 alloy steel. The bolt carrier group has a staked gas key, and the exterior finish is matte black oxide while the inside is chrome plated.

The flashhider is similar to those that come on Ruger's Gunsite Scout bolt action and Mini-14 autoloader. It can be swapped out for other muzzle accessories.

The trigger is a single-stage unit. The pull weight of ST's sample averaged 7.5 pounds.

The carbine comes with an A2-style post front sight that's adjustable for elevation.

A flip-up, windage-adjustable Ruger Rapid Deploy rear sight is available with the AR-556.

One 30-round Magpul PMag polymer magazine comes with the carbine.

The best single five-shot 100-yard group came with Black Hills 52-grain Match ammunition (0.95 inch), and the carbine's overall average for seven factory loads ranging in bullet weight from 52 to 69 grains was a very respectable 1.79 inches.