May 2, 2012

Ruger SR556 5.56 NATO/223 Rem.

There’s no doubt about it; the AR-15 has gone mainstream. Over the last several years, the growth in demand for black rifles has lured many manufacturers (including the big guys) to introduce their own versions of the venerable Eugene Stoner direct-gas-impingement design. Now that the market has matured, Gun Tests magazine is seeing engineering departments introduce versions that are claimed to improve upon the original AR-15 through the use of gas-piston systems.

They recently tested the Ruger SR-556FB, $1995.

Here's what they said:

In the original AR-15, gases are vented back through a gas tube to work the bolt and bolt-carrier group. The entire assembly works as its own piston. Since all of the gas is vented back to the bolt, fouling and heat build up in the mechanism. A piston system uses exhaust gas to work an exterior piston and operating rod assembly, greatly reducing the amount of spent gas that reaches the gun’s action. In our tests all three of our guns ran with less fouling than we see with our regular AR-15s.

The Ruger SR556 uses adjustable gas pistons, allowing the user to change the piston setting to optimize its operation for different ammo and operating conditions.

How We Tested

All of our testing was done in the climate-controlled atmosphere of Bass Pro Shops in Grapevine, Texas, sparing us from the ravages of a record cold snap. We started by mounting a Sightmark 3-9 X 42 (SM13016) Scope on a LaRue Tactical LT-104 QD Scope Mount. This lever-throw mount allowed us to move the scope quickly but securely among our flat-top equipped test rifle. The Sightmark had a smaller frame that balanced well with our gun, and featured an illuminated reticle to aid in low-light settings. Our target range was 50 yards.

The second portion of our testing involved utilizing iron sights at a shorter distance of 25 yards. We proceeded to fire 30-round magazines at a range-limited speed of one round per second to evaluate the gun’s handling and responsiveness in a dynamic situation.

Gun Tests March 2010


Ruger's entry into the competitive AR-style market offers a complete package of quality features, which are also noted in its upper-tier price. Its performance was solid and trouble-free. A heavy trigger pull was Gun Tests' primary quibble.

After that, we also checked to see how cool the gun ran. The primary claims associated with gas-piston guns are that they run cooler and cleaner than comparable AR-15 direct-gas-impingement designs. It was fairly easy to disassemble the gun to look for carbon build-up, but verifying operating temperatures required a different approach. We devised a test protocol for this measurement through the use of an infrared thermometer. We decided on three points of measurement for our gun: the bolt, the chamber, and the end of the barrel. We verified the room temperature and the surface readings on the gun prior to testing. Then 30 rounds were fired through the gun and surface temperatures were taken immediately thereafter. The Ruger showed temperature changes of 8 degrees and 4 degrees, respectively.

We could see that there could be long-term benefits in the cooler operating temperature of the gas-piston system, although we did not see the AR rise to an exceptionally high level. A more extensive thermal test will be conducted in the near future.

Here’s how the rest of our evaluation turned out:

Ruger SR-556FB Model 5902 5.56mm NATO/223 Rem., $1995

Ruger’s foray into the AR market was announced with a flourish in May 2009. Instead of entering the crowded realm of AR-15 clones, Ruger chose instead to design its own proprietary semiauto piston system and incorporate it into full-featured offering. The SR-556FB comes only one way from the factory and that is fully equipped. It appears that Ruger attempted to cater to the new AR owner by making a number of equipment choices for the buyer.

The SR-556FB sought to differentiate itself from other black rifles right out of the box, cradling the gun in a custom cloth case with the red Ruger logo on full display on its front. The case wasn’t bad, but we’d like a bit more padding and a much heavier zipper than the one on our sample. Our gun also included a pair of Magpul polymer 30-round magazines, a design we found to be quite dependable.

Gun Tests March 2010


The Troy Industries Folding Battle Sights provided a solid set of back up irons. Gun Tests liked this sort of configuration because it allows them to be co-witnessed with red dots and other CQB optics.

Beginning our inspection, we found that the 16.1-in. barrel was chrome-lined and made of chrome-moly-vanadium steel and (thankfully) topped with an AC-556 flash suppressor. These parts were all manganese-phosphate coated along with the gas block and regulator. The lower receiver was made of aluminum and hard anodized. Ruger chose to chrome-plate the bolt assembly, which made for a nice appearance. The Ruger emblem was also engraved on the bolt as well. In fact we noted the Ruger logo appeared in no less than eight different places on our test gun—a definite branding effort.

The SR-556 had the standard AR-15 configuration of charging handle, mag release, dust cover, forward assist, and left-side-only lever safety. The stock was Ruger-branded, but was the standard M4 variety as well.

The other parts of SR-556 were upgrades over a standard AR. A comfortable Hogue Monogrip adorned our gun, and a Troy Industries 11-in. Quad Rail wrapped around the barrel of the Ruger. This left plenty of space for all manner of accessories to be mounted. Troy Folding Battle Sights graced the top of our gun. The rear sight had dual apertures and was adjustable for windage, and came paired with a partially hooded front that offered elevation adjustment. We like this sort of sight configuration because it allows them to be co-witnessed with red dots and other CQB optics. This additional hardware, along with a heavier piston system, brought our gun in at 7.9 lbs.

The trigger on the SR-556 was a single stage version that broke very cleanly, but at a rather robust 8 lbs. We’d like at least a couple of pounds shaved off this pull weight.

Gun Tests March 2010


Gun Tests found the Hogue Monogrip on the SR-556FB to be comfortable and secure.

The primary design difference between the SR-556 and a standard AR-15 is the Ruger proprietary gas piston system. The transfer or op rod was noticeably larger than a standard gas tube and was electroless tin plated. The gas block has a rotating dial on its end with four positions labeled 0 thru 3. This allows the gas output to be tuned to optimize the gun’s action with a variety of ammunition. At the fully open or 0 position, the gun becomes a single shot. For our purposes, we found the middle or 2 position worked well with all of the ammo we tested.

Accuracy testing revealed the Ruger handled all of our ammo relatively well, turning in its best group with the Remington 55-gr. MC at 1.2 inches, and fared only slightly worse with the heavier 63-gr. Silver State loading. Recoil was dampened well, and the gun functioned with no malfunctions. The Ruger SR-556 also fared well in our action shooting. The Troy sights proved to be much easier to line up and adjust than other models. We found the gun to be steady and relatively easy to point, although our testers did find the gun to be balanced pretty far forward because of the long quad rails.

Gun Tests Team Said: It was obvious that Sturm Ruger spent quite a bit of time on the design and execution of the SR-556. New shooters will find its package well-equipped and easy to use. Experienced AR shooters will appreciate the inclusion of quality stuff that works.

Comments (27)

Just purchased 2 Ruger Sr556 E for the girlfriend and my self.
Going to use in the three gun shooting comp, in British Columbia
Enjoyed reading all your comments. Never had a rifle like this......

Posted by: A-S-Ex | July 23, 2014 10:12 PM    Report this comment

More spam.....!!!!!

Posted by: canovack | May 24, 2012 11:03 AM    Report this comment

I try to learn as much as I can from other's experiences, especially when it's from others who are or were 'in the trade' (no matter what trade). You fellas share regularly, most of you are more experienced in 'tactical' situations that I - by far. So I'm 'all ears' when we have these discussions, even though technically it's 'all eyeballs' as I only get to read what you post and not hear it. Anyway, thanks for sharing your experiences and opinions in such detail.

Posted by: david b | May 5, 2012 8:23 AM    Report this comment

As I often say, I learn a lot from you guys and I thank you for passing on your wealth of knowledge.

Posted by: Cecil B | May 4, 2012 11:24 PM    Report this comment

I don't necessarily think that piston operated systems are all good or bad, just as I don't think that all direct gas impingement systems are all good or bad. In my collection of tactical pieces, I have representatives of both systems, and as a normal shooter, I really don't favor one over the other. I figure that each system has its advantages and disadvantages, and the system that might be chosen for extended serious business by anybody, will likely depend on the environment and the amount and types of shooting that are to be done. One thing that's quite certain, though, is that if one is going to be in a situation of prolonged carry, use, and continued shooting, one had better have a pretty good cleaning kit and solvent/lubricant in order to stay active. That's one reason, by-the-way, that I have replaced all telescoping butt stocks on all of my tactical rifles. I have gone back to the rigid stocks that have a compartment and trap door in the butt stocks, and each rifle has its own cleaning kit inside the stock. That's what I had in Vietnam with my M-14 and my M-16. I never, ever want to be without the capability of cleaning and maintaining my weapons.

Posted by: canovack | May 4, 2012 8:04 PM    Report this comment

I greatly thank you guys for the info on the piston operated AR-15s.I think that I will pass on them as well!!

Posted by: NCSNIPER | May 4, 2012 7:26 PM    Report this comment

Trained at Knox '65-'66 and I developed a thorough dislike for the M-16.Thanks to that damn fool Mc Namara those things had to be cleaned nearly as often as loaded.Fired an old original recently, wrong ammo was the major contributor.
Historical note: Custer was plagued by soft .45-70 cases jamming trapdoor Springfields. The cases recovered at the battle site showed torn rims and knife marks. Of course being out numbered a few hundred to one by warriors ,better armed, and protecting their families didn't hel Custer and the 7th Cav.at all.

Posted by: snugdlo4 | May 4, 2012 4:54 PM    Report this comment

Amen Cecil!!

Posted by: IanFrog | May 4, 2012 2:31 PM    Report this comment

SKS and AK-47 were designed for steel cased ammunition. Chrome and oversized chambers was the design chosen. American battle rifles and carbines historically have been made to close and tight tolerances. M1 M14 M16 are precision devices. Examination of the fit of the gas piston in the M1 and M14 would reveal a very tight fit (minimum gap between the piston and the cylinder wall). Examination of that same gap in SKS and AK-47 is a real eye opener because there is such a large gap that one would wonder how any pressure was ever developed in the gas system at all. Examination of the gas port from the barrel reveals a huge hole compared to M1 M14. Obviously a non-precision gas system will not be affected by sand, mud, gunk as American battle rifles can be. In Viet Nam, it was not uncommon for GIs to abandon their M-16s and pick up an AK. Early M-16s were very ammunition sensitive and "Lowest Bidder" ammo that made it to VN did not burn cleanly and left enough gunk in the gas system as to render the M-16 useless unless constantly cleaned. A real hassle in combat. And M-16 were not provided with cleaning kits and the Army didn't see a need for them (assuming that only clean-burning ammmo would be used). SKS and AK-47 have very loose tolerances and rely on massive amounts of gas to operate. Gas is cheap. Just because a rifle is American designed, doesn't mean that in combat it is the best. Stoner attempted to get around the piston/gas cylinder problem by piping the gas back directly to the bolt and carrier. He designed it for clean burning ammo. He probably never considered what would happen if black powder was used for the propellant.

Posted by: PTHunter | May 4, 2012 2:11 PM    Report this comment

Without getting TOO technical, I figure that if you can take an AK, bury it in mud, wash it off with a garden hose and apply a little WD-40 and it shoots, steel cartridges probably won't screw it up. I know that is not an in depth analysis, but sometimes, the obvious is as simple as years of research.

Posted by: Cecil B | May 4, 2012 1:10 PM    Report this comment

Keep going, guys. I'm learning. Thanks!

Posted by: david b | May 4, 2012 7:33 AM    Report this comment

The Russians solved the stiction problem utilizing chrome plating of the chamber. As a manufacturing expedience, it was easier to also chrome line the barrel at the same time instead of trying to isolate the barrel from the chamber. There are many ways to skin a cat. The Germans and Japanese had supply problems and chrome may have been difficult to obtain at the time. Broaching a chamber is a simple process and final chamber reaming to set head space is much easier on steel. If the chamber is oversized, and head space is sloppy, chrome plating will work "OK". We don't know all the conditions that affected the decision to select fluted chambers or chrome plated chambers. Obviously they both work.

Posted by: PTHunter | May 3, 2012 11:42 PM    Report this comment

For someone who thought they were fairly knowledgeable about AR type rifles all I can say is Doohhh! I thought the piston systems were the greatest thing since sliced bread. Now I'm glad I haven't been able to afford one! Like my bushy just fine anyway even though it's a Carbon 15 model. Heard some bad things about them but never had a problem. The staking is well done and there's a lot to be said for light. Unfortunately it is proprietary so as far as parts go...well you all know the answer. I've never had the need but figured I could probably modify it if needed but it wouldn't be cost efficient. Got it for a decent price and added rails and stud for a bipod if I ever want to use one. Guess turning wrenches all those years was good for something. I never knew that about steel cased ammo PThunter, thanks for the info. I love Rugers and have a special place in my heart for my GP100 although I prefer a 1911 for carry and most anything else but even at 1500.00 American I can't believe it has an 8lb trigger! A little polishing and JP springs smoothed out the trigger on mine to acceptable. I just hope you all don't get tired of me here too soon cause I can be hard to get rid of....After reading the comments here I think I'll stick with Mr. Stoners original design. As for steel cased ammo, I've shot a few rounds that someone gave me with no problems but since I can't reload it I certainly wouldn't buy any. All I have to do now is find someone with a german or jap WWII firearm so I can check out the chamber. Take care all and thanks again for the info.

Posted by: BadDoggie | May 3, 2012 11:27 PM    Report this comment

So, here is a dumb question. Why does steel ammo not malfunction in an AK? Not being a wise ass, just would like to hear from someone that knows.

Posted by: Cecil B | May 3, 2012 11:09 PM    Report this comment

That's some very interesting, and important information to know, as concerns steel cased ammo. I've been posting in this forum for several years, and I am never disappointed in the information that is freely exchanged between subscribers.

Posted by: canovack | May 3, 2012 8:49 PM    Report this comment

just want the updates

Posted by: david b | May 3, 2012 7:11 PM    Report this comment

Steel cased ammo requires a different design chamber because the steel case does not "spring back" from the chamber walls (as brass does)when the pressure drops and it cools. Steel simply does not return to the pre-fired diameter and actually maintains an outward pressure due to a spring-like effect on the chamber wall. Think "Stuck like glue". During WW2 both the Germans and the Japanese used steel cased ammo. They solved the extraction problem by fluting the inner surface of the camber to reduce the amount of surface that the steel would encounter as the cartridge fired. This extraction problem was even more serious in the machine guns so the fluting was more pronounced. If you have access to a WW2 Mauser rifle, look very carefully in the chamber with a strong light and you will see the fluting. If you go to a rifle range often enough you will find somebody firing WW2 ammo through a Mauser. Pick up and examine the fired case and you will clearly see what looks like fine lines (bright metal) running lengthwise around the outside of the entire case. Steel 9mm ammo is not too prevelant, but if you see someone firing it in a P-38 or a Lugar, pick up and examine a case. You'll see the lines easily. If you look closely you'll probably see the lines in brass cases too. Firing steel in a gun designed for brass will invariably cause the extractor claw to be ripped out of the bolt. If you are lucky, it only tears the claw off the extractor and doesn't damage the bolt.

Posted by: PTHunter | May 3, 2012 5:59 PM    Report this comment

DO NOT USE Steel case ammo. My two sons have these rifles, and both jam when using steel cased ammo. Usually a cleaning rod up the barrel will dislodge it (cringe), but one of the guns jammed up so bad a gun smith had to extricate the jammed cartridge. After a $200 bill, and a warning from the gun smith "that piston guns don't like steel cases", both boys switched to brass ammo only. I think I heard that the lacquer or polymer coating on steel cases is the problem - especially after the chamber warms up. On the other hand, my rock river AR (gas) eats everything without a quibble.

Posted by: woodhead7 | May 3, 2012 5:11 PM    Report this comment

DO NOT USE Steel case ammo. My two sons have these rifles, and both jam when using steel cased ammo. Usually a cleaning rod up the barrel will dislodge it (cringe), but one of the guns jammed up so bad a gun smith had to extricate the jammed cartridge. After a $200 bill, and a warning from the gun smith "that piston guns don't like steel cases", both boys switched to brass ammo only. I think I heard that the lacquer or polymer coating on steel cases is the problem - especially after the chamber warms up. On the other hand, my rock river AR (gas) eats everything without a quibble.

Posted by: woodhead7 | May 3, 2012 5:02 PM    Report this comment

Note that this test is dated 3/2010. A quick online search finds this models street value is more like $1500 nowadays. Considering the high quality accessories added to a solid foundation, that's just about right - unless you factor in the $150 to $200 for a good trigger...eh, not such a smokin' deal.

Posted by: Dragonchow | May 3, 2012 1:49 PM    Report this comment

Ruger has always been one of my favoite guns, mainly because they are made right here in the good old USA. But thier prices have been getting a bit on the to high side for the good hard working person and those that have to live on fixed incomes ie; the disabled and elderly, they seem to be going for the elete type people now. there is just no way this old fart can afford 2K for it. God Bless America and Our Troops Past Present and Future.
Keeping to My Oath Locked Loaded and Keeping My Powder Dry.
Get the US Out of the UN and the UN Out of the US.

Posted by: bear1 | May 3, 2012 1:43 PM    Report this comment

Piston powered AR15 hmmm? The problem with with this design is, that it places excessive stresses on the upper receiver, and barrel. Don't belive me? Look at the M-1 Garand, M-14, M-1 Carbine, FN Model 1949, Tokerev Rifles, and the AK 47. All have robust receivers (more so than any bolt gun), and barrels to the gas port to maintain accuracy. Gene Stoner moved all of the energy to the bolt carrier were it does the most good, and at the same time greatly reduced the stresses on the receiver, and barrel. That's why it's as light as it is. In the mid 1970's the US Army took 10 new non issued M-16A1 rifles, and without cleaning them shot them till they stopped. The average number was between 6,500-7,000 rounds of various GI Ammo. Who needs a piston?

Posted by: lotoofla | May 3, 2012 1:37 PM    Report this comment

Wow. That's a hefty price tag especially considering what one can get just above or below that $2k number. 8# trigger pull?? What is the reasoning behind that. Accuracy could sure be better for that kind of $$. The AR market is a mature market and it will be interesting to see how Ruger does considering the pricing.

Posted by: jaybirdjtski | May 3, 2012 1:05 PM    Report this comment

At this price level, Ruger appears to be targeting the other-peoples'-money market with the likes of SIG and FN. It appears to be a great rifle, but I don't see why it is worth double what a Bushy goes for.

Posted by: montemanm1 | May 3, 2012 12:05 PM    Report this comment

Sounds like a great rifle but with a market flooded with black rifles of high quality for half this price why would someone buy this one in these challenging economic times??

Posted by: IanFrog | May 3, 2012 10:49 AM    Report this comment

Any thoughts on how this gun will be able to be sold in California with it's 10 round, non-removable (without tool) magazine limitations?
Larry L (obviously in CA)

Posted by: PTHunter | May 3, 2012 10:38 AM    Report this comment

This sounds like an interesting rifle. That said, however, with as many pieces as I already own, it's not likely that I'll be adding this one to my collection.

Posted by: canovack | May 2, 2012 11:01 AM    Report this comment

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