Ruger SR-556 AR-15 Style 5.56mm Semi-Auto Carbine


by Jeff Quinn

photography by Jeff Quinn & Boge Quinn

May 15th, 2009




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While visiting the New Hampshire Ruger factory back last December, I was there to look at and shoot their new LCR .38 Special revolver, but while we were there, the Ruger marketing and engineering folks also brought out a couple of prototypes of their new semi-auto AR-15 style rifle, called the SR-556. There were five writers there that day, and of course, we were all sworn to secrecy. Ruger decided to introduce their new rifle at the 2009 NRA Show in Phoenix, and my sample SR-556 arrived here just a few days before.

The AR-15 has been very popular with a lot of shooters for many years now. The basic design is over fifty years old, and selective-fire versions of the AR-15 have served our military admirably for decades now. There are some folks who seem to hate the design, blaming the rifle for failures more related to the ammunition than the rifle design, but the fact is the rifles work well when maintained well, and are relatively light weight and easy to shoot. Anyway, the AR-15 is probably the hottest-selling rifle in the United States right now, and for good reason. I outlined in a piece titled “Homeland Security” a few years ago why every American should own an AR-15. It is important for every citizen to know how to properly use and maintain our nation’s main battle rifle, and if it ever comes down to it, spare parts and ammo are as close as your local National Guard Armory. The outcome of our recent Presidential election has spurred the biggest run on guns and ammunition that our nation has ever seen. Even folks who voted for Obama are now scurrying to buy firearms and ammunition while they still can, taking him at his word that he wants to ban all semi-automatic weapons from citizen’s hands. All over the country, ammo and firearm sales figures are up dramatically, especially semi-automatic rifles and pistols, and AR-15 sales are leading the pack.

There are many brands of AR-15 style rifles from which to choose, and most of them are pretty good. The design is a solid one, well-proven, and most manufacturers do a good job of putting them together. However, there are differences, and a few makers produce a product that will exhibit superior accuracy, or have a better trigger, or possess other features that might endear a particular rifle to a particular shooter.

Enter Sturm, Ruger, & Company with their new SR-556. Ruger is not new to the semi-auto rifle market. Their 10-22 is the most popular .22 Auto on the market. It is light, reliable, affordable, and accurate. The Mini-14 design has been around for decades, along with the selective-fire version of that rifle, the AC-556. Both are very reliable weapons. However, there is no denying that the AR platform is more popular these days, and Ruger has chosen the ideal time to enter head first into that market. Not content to just produce another “me too” AR-15,Ruger has taken the time, money, and effort to produce what is in some ways a superior product. I am not one who is constantly complaining about the AR-15’s direct gas impingement system. It works pretty darn well, and I have several ARs which perform perfectly, and give me no problems at all. There are a few AR manufacturers that have taken the basic AR-15 design, and replaced the gas impingement system with a gas piston system. Both systems work well, but Ruger has developed a gas piston design that is very versatile, and should prove superior under adverse conditions to both the gas impingement system and other gas piston systems. The gas system on the SR-556 is adjustable. There are four positions on the gas adjustment knob, numbered from 0 to 3. The 0 position shuts off the gas that is bled from the barrel to operate the action. In this position, the rifle acts like a straight-pull bolt action, and the action must be manually cycled. This is a good idea for training a new shooter on the AR design, as the rifle will not self-load after each shot. Also, if for whatever reason you do not want to leave a piece of brass on the ground, you can set the knob to 0 and the case will not be ejected. The standard position for most ammunition with be the number 2 position. The numbers 1 and 3 positions have gas ports that are slightly smaller and slightly larger than the number 2 position, respectively. The number 1 position is useful if the ammo is on the warm side, bleeding off a bit less gas, and cycling more gently than the standard number 2 setting. If the weapon has become dirty from shooting, or from blowing silt and sand, or if a batch of weak ammo is encountered, the number 3 position will bleed off a bit more gas to operate the action with more authority. This system reminds me of the adjustable gas system on the legendary FAL rifles, which have served all over the world, and are still in service by some military units. In practical terms for the average shooter, the adjustable gas system on the SR-556 allows the shooter to adjust the system to perfectly suit the ammunition being used. Setting the adjustment to the number 1 setting allows for a “softer” function of the rifle, and should reduce wear on the operating system. If a good deal is found on some ammo that is not up to NATO specs, no problem. Just set the adjustment to a higher number, and the rifle should function reliably with the bargain ammo. In a more serious situation, finding yourself with a filthy, dry weapon could get you killed. Having an adjustment setting that will allow the rifle to operate under adverse conditions might make the difference between coming in first or second in a fight. The gas piston system that Ruger uses is also very simple and easy to clean. Rotating the adjustment to where the flat side is on top allows the adjustment knob and piston to be pulled out. It can be done without tools, or by using a cartridge or other tool to rotate the knob. The piston is a two-piece design, and is about as simple as such a thing can be. There are no small parts to lose, and the rest of the disassembly for maintenance is like any other AR, also very simple. I like simple.

Other features of the SR-556 make the rifle more user-friendly. There are several inches of Picatinny-compatible rail for attaching optical sights, bipods, flashlights, lasers, forward grips, or any of the other multitude of AR accessories available on the market. The Troy Industries rails and hand protecting rail covers work very well, and are also very good-looking features of the SR-556. The rifle is equipped with superb folding sights, also manufactured by Troy Industries. The rear is adjustable for windage correction, and has two apertures for close and medium ranges, and the front folding unit is adjustable for elevation correction. Both sights fold down with a push of a button, and flip up instantly when needed. The full-length top rail accommodates just about any optical sight imaginable, such as the excellent Trijicon Reflex shown here. I absolutely love the Reflex, and this new one is much improved over the original. The new Reflex has a tritium dot that is always “on” and never needs batteries, like the original, but the new design uses a fiber optic illuminator to brighten the dot as available light increases. This allows the dot to be dim enough that it is not blinding in low light, but the illuminator brightens the dot brilliantly for use even in bright sunlight. Perfect.

The SR-556 wears a hammer-forged sixteen and one-eighth inch barrel, and the muzzle wears an AC-556 flash suppressor, which has proven to be very effective for many years. Good choice. The Troy Industries Quad Rail handguard is pinned to the upper receiver, and serves as a rigid guide for the gas piston. The SR-556 wears a six-position AR buttstock, which is an excellent choice, making the weapon very versatile, and able to fit shooters of all sizes, and allows easy adjustment for compact storage, or for use in tight quarters. Since this question is bound to be asked, yes, the SR-556 fires both 5.56x45mm NATO and .223 Remington ammunition, and I fired the weapon with both, using a wide variety of bullet types and brands. As many types as I had available, I fired for function testing, and fired several of those for accuracy testing also. The SR-556 weighs in at seven pounds, fifteen ounces empty, and is soft on the shoulder, even for a 5.56/.223 rifle.

For accuracy testing, I mounted my Leupold Mark 4 8.5 to 25 power scope, as this baby allows me to see just how accurate a rifle can be. Optical clarity and target definition is outstanding using this scope, and since I am far from being an expert shooter, I like all the help that I can get. The goal is not to see how well I can shoot, but to show the accuracy potential of the subject rifle. I fired for groups at 100 yards, and every brand tested displayed very good accuracy from the SR-556. The barrel has a one-in-nine inch rifling twist, and all bullets exhibited perfect stability, even the long seventy-five grain boat-tail bullet used in the Wolf Gold Match ammo. I fired for velocity readings with the chronograph set at twelve feet from the muzzle. Velocities are listed in the chart below in feet-per-second (fps), and all loads were fired at an elevation of approximately 400 feet above sea level, with an air temperature of around seventy-three degrees Fahrenheit, with low humidity. Bullet weights are listed in grains. FMJ is full metal jacket. SP is a soft point jacketed bullet. The Extreme Shock loads are specialty ammunition, made for extreme performance upon impact. The Extreme Shock 100 grain load is a low-velocity specialty heavy bullet round that did not prove suitable for this rifle, or any other 5.56mm/.223 that has a standard length throat. It is listed for information purposes only. As I have had this rifle only a short time, no attempt was made to develop handloads for the weapon. I just grabbed what I had on the shelf and went to work. However, I did send a lot of lead down range through this SR-556, and accuracy improved as the barrel seasoned from shooting. Accuracy readings are for three-shot groups, fired from a Target Shooting, Inc. Model 1000 rifle rest, and are listed in inches.

Ammunition Velocity Group Size
Winchester USA 62 FMJ 2879 1.375
Winchester USA 55 FMJ  2858 1.75
Extreme Shock 62 FHVL   2712 1.75
Extreme Shock 55 SRT  2453 1.18
Extreme Shock 100 ASP  1071 Not Tested
Black Hills 55 SP  2901 0.75
Wolf Gold Match 75 BTHP 2495 0.875
Mag Tech 55 FMJ 2909 1.18
Buffalo Bore 69 Sierra 2839 0.675

I was both pleased and surprised by the accuracy displayed by the SR-556. The rifle has a chrome-lined bore, and a standard AR trigger, both of which are usually not conducive to the best accuracy from the bench, but every load fired for accuracy in this rifle performed very well. While the SR-556 is built to be a fighting rifle, it has plenty of accuracy for competition or hunting. I continue to be pleased by the performance of the Wolf Gold Match ammo, and intend to take that ammunition and the SR-556 to the NRA Whittington Center near Raton, New Mexico later this month for some long-range accuracy testing, as well as the superb Buffalo Bore Sniper ammo. It has both high velocity and phenomenal accuracy.

The Ruger SR-556 comes with a padded soft carry case which has Velcro straps to secure the rifle inside, along with magazine pouches inside to store two magazines, and an extra pouch on the outside as well. The SR-556 is supplied with an instruction manual, padlock, and comes with three Magpul PMAG thirty-round magazines. Of course, the SR-556 can use any standard AR magazine, from the handy twenty-round Vietnam era surplus magazines which are my favorite, to the 100 round Beta C-Mag.

I am expected by some readers to be impartial, and to an extent, I am. If I have a problem with a weapon, I will always report it. However, while the market is flush with excellent AR style rifles, I am really excited about this one. I don’t know exactly why, I just am. I really like this SR-556, and I like the folks that are responsible for building it. From the CEO, to the marketing folks, to the engineers, to the men and women on the production floor, everyone that I have met at Ruger seems intent upon building quality products that shooters want. The SR-556 is an AR in a sea of many, but it has enough unique features to set it apart from the ordinary, and it should prove to be another instant hit for Ruger. Like all Ruger firearms, it is built in the USA.

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Jeff Quinn


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Adjustable gas piston design is simple and reliable.



Gas piston is easily removed for cleaning.





The SR-556 comes with three thirty-round Magpul magazines.





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Click pictures for a larger version.



Ruger SR-556 AR-15 style 5.56mm semi-auto carbine.





Pistol grip is a comfortable Hogue unit.



The SR-556 features Troy Industries' excellent folding battle sights.





There is plenty of Picatinny rail for mounting sights and accessories.



Rail covers protect the hand, and offer a comfortable hold on the weapon.





Buttstock is six-position adjustable.





The SR-556 uses the proven AC-556 flash suppressor.



Trijicon Reflex sight.



The SR-556 proved to be very accurate and 100% reliable with a wide variety of ammunition.