Ruger SR-556:


Ruger SR-556


Chrome plated two stage piston driven operating system. 4 position chrome plated gas regulator. Chrome plated bolt, bolt carrier and extractor. Cold, hammer forged, chrome lined Mil-Spec 41V45 barrel. 6 position telescoping M4 style buttstock. Hogue Monogrip pistol grip. Three Magpul 30 round magazines included. Troy Industries folding battle sights, quad rail handguard and rail covers.

ruger sr556 bolt carrier


  • Model: Model SR-556 M4 Type Semi Automatic Rifle
  • Mfg Item Num: 5902
  • Finish: Black
  • Action: Semi-Automatic
  • Caliber: 223 Remington/5.56 NATO (Note Ruger actually specifies both calibers suitable for this weapon)
  • Barrel Length: 16"
  • Capacity: 30+1
  • Trigger: Standard AR-15
  • Safety: Standard AR-15 Lever
  • OAL: 32 3/4"-36"
  • Weight: 7.92 lbs
  • Buttstock: 6 Point Collapsible

Ruger SR-556 Barrel and Gas Adjustment

SR-556 Troy Battle Sights Article

Ruger SR-556

The increasing interest in the AR-15 series of rifles and carbines has created a controversy whether the AR should have a gas impingement or gas piston operating system. While the AR certainly stumbled in its early days, its system has certainly been perfected, but it does require consistent maintenance to keep it operating properly.

The largest criticism is how the direct gas system blows debris from the fired cartridge back into the operating system, primarily the bolt, which collects to the point that it can actually slow the action or stops the gun completely. Admittedly, this would take a while, probably in excess of a thousand rounds on a well-made gun, which would not be a problem for the legally armed citizen or law enforcement officer, but for the soldier in a battlefield situation it is certainly problematic.

Ruger SR-556The obvious solution is to make sure that the dirt generated by the firing cycle never makes it into the action in the first place, which is why many knowledgeable folks advocate the gas piston action for the gun. This action is similar to the gas impingement but with an important difference — the gas created by the fired cartridge pushes a spring-loaded piston back toward the gun’s action and strikes an “anvil” attached to the bolt where the gas key was originally located.

This striking action cycles the bolt and keeps debris far away from the inside of the receiver. Sounds like a great idea, right? It is but the problem has arisen in the application of the system with some of the gas piston systems used to “upgrade” the AR being a bit small and fragile, and eventually breaking down with usage. Trying to retro-fit a gas impingement gun under standard handguards requires components that are sized to fit existing space, thus many such systems are not as robust as they should be.

The obvious answer is to build the gun from the ground up to work as a gas piston gun and to build the parts robust enough to stand up to the constant pounding the gun must take in order to depend one’s life on. Ruger has done this with the introduction of their new SR-556 model, and like all things from Ruger, it is built like a tank. Interestingly, Ruger has been making AR components for many years but this is their first entry into the AR-15 market and it looks to be a good one.

Gun Details

The SR-556 offers Ruger’s proven ruggedness and reliability while changing the AR-15 platform to a piston driven system. The gas piston driven SR-556 runs cleaner, cooler, and is easier to maintain than gas impingement rifles, offering significantly improved reliability due to the reasons offered earlier. The patent-pending two-stage piston driven operating system in the new Ruger SR-556 provides a smooth power delivery stroke to the action and vents combustion residue out of the bottom of the gas block.

Ruger SR-556When asked why Ruger decided on this system instead of a traditional gas impingement system, Product Manger Mark Gurney stated, “It’s a new gun, why go with an old system?” Makes sense. The four-position adjustable gas regulator allows the shooter to tune the rifle to specific ammunition and rifle conditions, minimizing recoil while maximizing reliability and long-term endurance.

Ruger’s Media Director Ken Jorgenson told me that the level of adjustment could be determined by where and how far the brass is ejected from the gun. A one-piece bolt carrier further enhances reliability with an integral transfer key that is also chrome-plated for enhanced reliability and quicker cleaning. Designed for long-lasting accuracy, the heavy contour, 16.12-inch chrome-lined barrel is cold hammer forged from Mil-Spec 41V45 Chrome-Moly-Vanadium Steel. The barrel has a 1-in-9-inch twist rate and is capped with an AC-556 flash suppressor giving the SR-556 a distinctive Ruger look.

The SR-556 is chambered in 5.56mm NATO, thus the Ruger SR-556 will also fire .223 ammunition with complete safety and reliability. A one-piece 10-inch Troy Industries Quad Rail Handguard provides ample room for mounting sights, optics and other accessories and is made exclusively for Ruger. This SR-556-specific handguard is pinned to the upper receiver for added durability and provides a rigid mount for the piston driven transfer rod.

The SR-556 is also equipped with Troy Industries Folding BattleSights, which will keep them out of the shooter’s field of view when enhanced optics like a Trijicon ACOG or Aimpoint red dot sight are used. These rugged, high-quality sights co-witness with Mil-Spec optics, and are easily removed or replaced. The sights can also be folded down with the push of a button or quickly flipped up with your thumbs.

The windage adjustable rear sight includes an instantly converted short and long-range aperture, and the protected front sight is elevation adjustable. I asked Mark Gurney why Ruger opted to go with such high-end accessories and was told, “We needed a specifically built forend to house our gas piston system and since we wanted to offer our customers a truly unique gun, we opted for the best we could find.” In addition, the Ruger SR-556 is equipped with a six-position telescoping M4-style buttstock that houses a Mil-Spec buffer and spring. A Hogue Monogrip pistol grip and three Troy Industries Rail Covers provide a comfortable and ergonomic grip when carrying or shooting.

Long life and performance of the SR-556 is enhanced with the use of high-performance finishes, which deter corrosion and add lubricity. The barrel and gas block are chrome lined, while the bolt, bolt carrier, and extractor are hard chrome plated. This makes cleaning these areas much easier and quicker as well as aiding reliability.

Ruger SR-556The flash hider and the exterior of the barrel, gas block, and regulator are manganese phosphate coated for added durability and a business-like appearance. While some may desire a traditional AR-style bird cage flash hider, I believe the Ruger Mini-14 version gives the gun a distinctive Ruger look that separates it from other similar rifles. Todd Wilkinson, Chief Engineer-Rifles, who was deeply involved in the gun’s design, told me that this was the exact reason they opted to use their proven flash hider.

All of the aluminum parts used in the gun’s construction are Mil-Spec hard coat anodized. The SR-556 is supplied with three, 30-round Magpul PMAG magazines that are some of the most reliable magazines ever built. The demand for PMAG’s is quite high and Ruger made a good choice in using these quality pieces of kit. These durable and lightweight magazines feature a storage/dust cover, a stainless steel spring, and a self-lubricating, anti-tilt follower for enhanced feed reliability.

The flat top upper receiver and barrel assembly are specific to the Ruger SR-556 while the lower receiver is built with Mil-Spec components including a single-stage trigger. The lower receiver is compatible with AR-style magazines, grips, buttstocks, and trigger assembly components so aftermarket products can be used to better fit the end user. The Ruger SR-556 comes from the factory in a quality padded carrying case that features the Ruger logo, hook-and-loop fasteners to stabilize the rifle within the case, and internal magazine pockets.

Range Time

Like any product designed to perform, features and looks are one thing, but it’s how the gun runs that is important and the first thing we need to know is how accurate the gun is. To find out, I contacted Leupold and had them send one of their scopes from the MR/T series, in this case a 2.5-8×36 Mark 4 model.

This variable power scope would give me both up close capability as well as some “reach” for targets at greater distances. More and more serious operators are selecting variable power optics for their individual long guns just for this purpose. The greater versatility that can be placed into any weapons system, the more potential situations it can handle. Since .223 ammo is becoming more and more scarce, I opted to sight in the SR-556 with common FMJ ammo. As luck would have it, I was able to get the gun zeroed in 10 rounds and was able to perform an accuracy test.

Ruger SR-556Accuracy was tested at 100 yards from a bench rest using five rounds of various ammo styles. I was interested in seeing just how much bullet style and weight would affect accuracy, so I used everything from 53 grains up to 77 grains.

In all fairness, I must advise the reader if it were not for my loss of concentration that the super-accurate Federal BTHP would have posted a sub-MOA (minute of angle) group with four rounds clustering into a 0.75 of an inch hole. After seeing how well I had shot the first four rounds, I committed the rookie mistake of becoming overly excited and lost focus on the last round with the resulting single flier. One is never too old to continue the practice of fundamentals.

This being said, the SR-556 proved to be exceptionally accurate with all of the loads tested regardless of weight, manufacture or bullet style. Over the years I have seen a number of guns that preferred one style of bullet over another meaning that one needed to find particular ammo in order for their gun to perform its best, but this was not the case with Ruger’s new rifle as it worked equally well with all loads tested, posting near MOA performance when combined with the excellent Leupold optic.

During testing of this two-part gas piston system, thousands of rounds were fired without cleaning and without failure. The piston driven transfer rod is electro-less nickel/Teflon-coated, which adds lubricity to the parts that do build up a great deal of crud as the rifle is fired. Yes, the bolt assembly remains relatively clean, but the gas piston components foul quickly with the dirt and grime that are expelled as the cartridge is fired. No gun runs clean so expect to scrub these components at some point. This being said, I believe it is safe to say that any AR will stop running due to a fouled bolt assembly before a fouled gas piston but only time will tell.

I continued to test the SR-556 for the remainder of the day, performing a number of combative carbine drills and basically getting in a solid practice session with the new gun. Since I was at my gun club, a number of folks happened by and noticed that I had something different and begged me to shoot the gun.

While it was a bit hard on my dwindling ammo supply, I let everyone who asked take a run at it. At the end of the day, the SR-556 had digested over 1,000 rounds without a single “burp,” and with a barrel and action that was cool to the touch. Everyone who shot the gun had nothing but good things to say with the normal follow-up questions being “How much is it?” and “When will it be available?”

ruger8While testing the gun, I added several components that I felt enhanced its performance. The first was the new short quick attach forward grip from Ergo Grip and the second was the CTR stock from Magpul. While vertical forward grips are controversial I have found that having one gives me greater control of the muzzle as I move from target to target. The secret to using such a grip is not to grasp it like a beer can, but to keep the thumb on the outside and “cam back” just as you would if the hand were being used as support on a pistol.

The Magpul CTR is a superior adjustable stock as it locks solidly in place, offering as locking lever that removes any and all stock wobbles. The rubber buttpad is not used to tame the recoil of the 5.56, but keeps the stock from “walking” on the shooter’s shoulder in rapid fire. Both are worthwhile additions to any AR platform.

Final Notes

At the conclusion of a week of shooting the SR-556, I came away with a very positive opinion of the new gun. Did I have any druthers? Sure, I would like to see a budget model for those who want a basic carbine without all of the rails and other gizmos. While Troy Industries makes a terrific product, many people can get by with less and would appreciate the reduced cost. The folks at Ruger assured me that this is being considered.

With the demand for AR-15 weapon systems continuing to increase, I believe that Ruger will sell all of these that they can make and for good reason. It is a robust, solidly built, well thought out rifle that would be a good choice for the Special Forces Operator, law enforcement officer or the legally armed citizen. It is that versatile!