Ruger makes some well-known semiauto rifles, including the 10-22 22 LR and the Mini-14. But when the company rolled out the SR-556 in May 2009, it was the company’s first foray into an increasingly crowded and competitive segment. And just looking at the feature set, including the two-stage piston-driven action, shows us the company put a lot of careful thought into the initial build.
To begin: The SR-556FB had a heavy contour, 16.12-inch chrome-lined barrel forged from Mil-Spec 41V45 chrome-moly-vanadium steel. The 0.700-inch-thick barrel had a 1:9 twist rate and was capped with an AC-556 flash suppressor. Our testers preferred the closed-bottom design of the other two guns’ hiders because they’re less likely to kick up debris if the shooter is on the ground. Chambered in 5.56mm NATO, the Ruger SR-556 also fired 223 Rem. ammunition.
The barrel and gas block were chrome lined, while the bolt, bolt carrier, and extractor were chrome plated. The piston-driven transfer rod was electroless nickel/Teflon coated. The flash hider and the exterior of the barrel, gas block, and regulator were manganese-phosphate coated. All aluminum parts were Mil-Spec hard-coat anodized.
The gun specs say the SR-556 comes with a one-piece 10-inch Troy Industries Quad Rail Handguard, but ours measured nearly 11 inches in length. Added to the Mil-Spec rail on top of the receiver, we counted almost 50 inches of rail surface to mount flashlights, lasers, grips, or perhaps a small barbecue pit. The handguard is pinned to the upper receiver and provides a mount for the piston-driven transfer rod. Three Troy rail covers provide a comfortable gripping surface.
On top, the SR-556FB is equipped with Troy Industries Folding BattleSights (thus the FB in the name), which our test team lauded above. They co-witness with Mil-Spec optics, and are easily removed or replaced. Pushing in a spring-loaded button on the right side of the sights allows them to be folded down or flipped up with one hand. The windage-adjustable rear sight includes two apertures, and the protected HK-style front sight is elevation adjustable.
At the butt is a six-position telescoping M4-style buttstock like we found on the other guns, but the Hogue Monogrip rubber pistol grip provides a better trigger-hand shooting surface than the other guns, our team thought.
Ruger’s published specs for the gun say it weighs “7 lbs. 15 oz.” without a magazine, but ours apparently was still carrying around turkey, and the scale dinged at 8.4 pounds without a magazine and 9.4 pounds with a loaded 30-round Magpul PMAG magazine in the maw. The gun came in a padded Ruger-branded carry case with hook-and-loop fasteners and internal magazine pockets. Ruger says the gun ships with three 30-round Magpul PMAGs, but our gun had only two. Even with two, the SR-556 still had an edge over the Stag’s and the High Standard’s one supplied magazines.
Of course, the heart of the gun is the patent-pending two-stage piston-driven operating system. Ruger claims it delivers a “smooth power delivery stroke to the action and vents combustion residue out of the bottom of the gas block.” The four-position adjustable gas regulator allows the operator to tune the rifle to specific ammunition and rifle conditions. In fact, at one point we dialed it down so that shells barely cleared the ejection port and we could more easily scoop up brass.
As a latecomer to the AR fray, it makes sense that Ruger skipped the DIG system and jumped to the piston system, at least in terms of current thinking. As you might guess, we’re skeptical about the superiority of the piston system’s reliability, but we don’t have data yet to back up that skepticism. Time and the market will shake that out. What we do know is that properly maintained DIG ARs are reliable because there’s nearly half a century of data to back that up, and they are made by some well-thought-of companies, including Bushmaster, Remington, DPMS, Stag Arms, Smith & Wesson, Armalite, Lewis Machine & Tool, Colt’s, Knight’s Armament Co., and LaRue Tactical, to name a few.
Moreover, we recognize that the GPS choice likely creates tradeoffs in the SR-556 that consumers might not want. Something makes the Ruger heavier than the other guns in this test—perhaps some of it is the gas system, or the rails. But a pound is a lot—12% more than the Stag—and that weight sits forward. As a result, our shooters said the Stag and HS guns handled better.
The Ruger turned in the best performance with the SSA ammo (1.11 inch AGR), but it also had good results with the Federal FMJs, as we noted above. We also liked that it had smaller maximum spreads than the Stag. In our view, the gun’s 9.4-pound trigger certainly held back some of its accuracy potential.
But for the shooter who wants to include accessories in his kit, the Ruger easily beat the HS gun and, when optics were considered, it beat the Stag, too. The Troy rail system easily accommodated a riflescope, red dot, and laser. The Stag and HS guns could use a riflescope, but not the other optics because the front sight fixture blocked them. However, the Stag could use a laser on the side rails or bottoms, but not a red dot on top, unless we bought a special mount.
Our Team Said: One of the things that our testers worried about is whether the new SR-556 is completely debugged. In our tests, we had one early blip with the gun that didn’t repeat, so this worry wasn’t backed up by problems we can point to. Elsewhere, the Ruger is heavier and more expensive than the others, but it offers a heckuva lot of value that the DIG guns didn’t. Our team would pick the SR-556 ahead of the High Standard gun by quite a lot—rails, sights, and supplied magazines were major benefits the Ruger enjoyed. The Stag vs. Ruger choice is a lot tougher. The Stag was lighter, but the Ruger’s rail system and sights were much better. The Stag was slightly more accurate with the Monarchs but slightly behind with the SSA ammo, and both it and the Ruger shot very well with the Federals, so with the right ammo, accuracy is a coin flip. So, we’ll leave the choice like this: Both the Ruger and Stag guns get A- grades, and the shooter can decide for himself if he wants to pay more for the Ruger’s features.
