Sig-Sauer 556

Sig 556 Rifle:

Submitted by .40Smith

Nothing will get a gun enthusiast’s eyes rolling faster than an ad campaign for a new product that starts off with “No other semi-automatic rifle has captured the imagination of the shooting public like…” And the Sig-556 certainly has its fan boys, as well as its haters.

When it first came out it was fairly expensive, hard to find, no aftermarket support and a few quality control issues from Sig. Still though, any fan of the Sig-550 Series rifles, aka the “Swiss Army Rifle”, would at least have to take a serious look at the Americanized 556. Sure, you can still get a real Swiss 551, but thanks to the insane import rules from prior legislation (signed by a Republican president by the way) as well as prior NFA restrictions, you’ll be looking at paying $10,000 to $15,000 for one, not including the proprietary $120 magazines. And those are pre-panic prices.

Perhaps the hype leading up to its release, the mystique of the Swiss rifle that it is based on as being the true standardized people’s army rifle, coupled with a general lack of familiarity from the majority of firearms enthusiasts, especially those in the AR/AK realm, caused some pretty polarizing reactions that persist to this day . The saying is “the Swiss don’t have an Army, they are an Army.” You are issued a full auto/select fire 550 series rifle and you take it home with you between drills. When you leave military service, you take your 550/551 to get converted to semi auto only and you get to keep it forever. It’s common for Swiss families to pass down gun safes with generations of military rifles in them. How cool is that? Of course that is why they lead the world in violence and gun crime. No, actually they are among the safest in the world, despite the anti-gun movement’s rhetoric here, but I digress.

With the import restrictions and price points in the civilian “AR” market, Sig decided several years ago to bring an Americanized 55X series rifle to market. They wanted functionally the same firearm, but something that took standard AR magazines. They also saw an opportunity to shave off a pound or so of weight by replacing the metal lower receiver with standard aluminum, but then they added half a pound more to the original excellent hand-guards, probably due to a combination of marketing and obscure regulatory compliance for mandatory differences, etc. While they were at it, they retooled the back of the receiver to take the standard M-4 stocks, that way they could mitigate the overall lack of aftermarket options right away.

Sig correctly recognized a significant demand for 55X series rifles in America, but then misjudged the fierce loyalty to the originals from the purists, as well as the suspicion of newcomers from the established AR base, thus electrifying the highly charged polarized reaction that’s only recently started to simmer down. Since then they’ve again re-retooled the back to take original Swiss 55X folding stocks, and have played around with various levels of optional trim like a railed out SWAT, a longer barreled Designated Marksman Rifle version, etc. So what are the pros and cons of the 556?


  • Sig 55X long stroke operating system
  • Sig 55X 2 position gas valve
  • 5.56 chambering
  • Uses AR magazines
  • Fairly good aftermarket support (finally)
  • Ambidextrous Safety standard
  • 1:7 twist*
  • Thin profile Melonite barrel**
  • Unique 2-stage factory trigger***
  • A little nose heavy****


  • More expensive than the average AR
  • Not as much aftermarket support as an AR
  • Weighs a little more than the average direct impingement AR
  • Slightly more recoil than the average AR due to larger gas system / reciprocating mass
  • Most stock iron sights are pretty crappy. This is a growing trend though, and even many AR’s offer shitty or even no irons at all and market their firearms as “optics ready.” This is mitigated by several high quality BUIS options now available and a much better diopter version coming standard on many 556’s from the factory.
  • Originally came with unnecessarily heavy hand-guards. Aftermarket or current factory guards fix this.
  • Had some legitimate though overly exaggerated QC issues from the factory
  • 1:7 twist*
  • Thin profile Melonite barrel**
  • Unique 2 stage factory trigger***
  • A little nose heavy****

A quick note on the quality control issues: This is a very polarizing rifle, and it was a little pricey, especially at first. And it came from Sig, which is held to a high standard in the first place. So it’s natural that any and every issue, no matter how tiny or rare, was emphasized with extreme prejudice. I’m actually cool with that because that’s the kind of consumer pressure that leads to better products in the first place. Some of the things that a “few” of the 556’s out there had issues with were:

  • Canted sight rails (Arsenal AK’s, widely regarded as some of the highest quality AK’s you can get, also recently had canted sight issues). This has been fixed.
  • Bolt carrier peening. This was a minor, mostly cosmetic issue that can be solved with 30 seconds of Dremmel / file / sanding work. It only affected a small part of the middle of the production run and has been fixed anyway.
  • A (very) few soft hammers. This has been fixed and is replaceable at the armorer level or under warranty.
  • A few with *slight wobble* between upper and lower. Doesn’t affect accuracy and can be “fixed” with one strip of electrical tape. Worst cases aren’t any worse than the stamped average AK.
  • A (very) few issues of unacceptable accuracy due to poor QC. , this was in the middle of the production run during the first great panic of ’08. This has been fixed and those caught in that part of the run have been warrantied to the satisfaction of most.

All these issues, except some of the cosmetic peening, have been reportedly covered by the Sig warranty to the satisfaction of most users. That doesn’t get Sig off the hook though. You buy a Sig rifle for Sig quality and you should get exactly that. Quarterly margins for the shareholders be dammed. That said, there are many AR manufacturers with the occasional issue as well, not to mention those inherent to the design itself.

Sig 550 bolt carrierSome say the 556 is the best of an AR and an AK. While there are AK’s out there chambered in .223/5.56, they typically don’t take AR magazines. Some are typically a couple MOA’s off in accuracy like any other AK due to its large operating system and its loser tolerances. The 556 splits the difference here, slightly tilted more towards the AR in accuracy but with core reliability closer to that of an AK. The tolerances aren’t quite as loose as an AK, but it makes up for this by having an easily actuated 2 position gas valve. Normal and “Adverse” settings so if it gets all gunked up, which isn’t likely because it runs cool and clean anyway, you can flip the switch and power through it until you get the chance to field strip it. If the AR has an Achilles heel, it’s the fairly flimsy bolt group and extractor. Hold up an AR bolt group to an AK bolt group and even the most rabid AR fan boy has to bow out of that one. The Sig 556 has a bolt group so AK I’m surprised old man Kalashnikov doesn’t drag them into patent court like Apple did to Samsung.

So if you want a fairly unique but accessory compatible 5.56 rifle with a clean, cool running long stroke gas valve, that’s fairly accurate and takes standard AR magazines, is made up with (mostly) ultra-long cycle life hard parts, take a serious look at the Sig 556. I took a 2 day operator class at the factory (back when an entire case of ammo XM 193 was included in the $400 fee!) and saw dirty and dropped 556’s shoot a total of 5-6000+ rounds among them between half a dozen students, and didn’t see a single malfunction of any kind. That doesn’t prove it’s a supergun by any means. But it does help put some of the overhyped criticisms in perspective. The course included everything from point-blank double taps to 300M scoped prone and everything in between. The rifle was as accurate as the shooter and with good match ammo it can get out there to Designated Marksman Rifle (400-600 yard) ranges with acceptable levels of accuracy with good optics and shooters.

It’s the American version of one of the most famous citizen soldier rifles in the world, where right now there are many hundreds of thousands in the homes of average citizens in a relatively tiny country. And that’s pretty damn cool if you ask me.

*Some folks who have or prefer 1:9 twist AR’s will knock 1:7 as being too tight especially for popular 55 grain ammo. But there are tons of AR out there that shoot 55 grain ammo with a 1:7 twist just fine. 1:7 is supposedly optimal in the 55 – 75 grain range. If you knew for a fact all you would ever shoot would be 55g, then maybe 1:8 or 1:9 would be slightly better, but only slightly. Anything heavier, like popular 62 grain and especially heavier match grade stuff and 1:7 really starts to shine.

**Some folks are addicted to chrome lined barrels but there seems to be a lot of misunderstanding about this. The main advantage of chrome lined is corrosion resistance. Not really a factor for 5.56 / .223 ammo since you have to look long and hard to even find corrosive ammo. Even if you do, you then have to use it and not clean it to realize this “advantage” and even then unless everything else the gas touches is also chrome lined, you have to clean it pretty soon after shooting it anyway or you’ll still get corrosion. As for wear and tear and long-term barrel life, Nitrite / Melonite is every bit as durable as the best chrome lining, and many say even more so. It’s as hard or harder than chrome, and since it’s impregnated into the metal, there is nothing to flake off over time. Put it this way: when was the last time you heard someone bitch about the poor quality and lack of durability of a Glock barrel because it wasn’t chrome lined? As for the thickness, it can be thinner (which dissipates heat better anyway) precisely because it’s Melonite and not chrome lined. If you research its sustained rates of fire you will be impressed. Unless you’re a bumpfire junkie, and even then you’ll have a hard time burning one up unless you try really hard.

***This, like any trigger, is a love it or hate it personal preference. Yes, it’s different, but not radically different and there are aftermarket options out there finally for that hair-trigger match grade thing if that’s your pref. I’d give it a “B+” for a stock trigger and a “C-“compared to most match triggers but as mentioned, you can adjust/swap it out anyway. If anything, it’s a tad on the heavy side, but you can de-spring it anyway.

****This is arguably another personal preference. Folks will spend in some cases hundreds of dollars on fancy muzzle devices to slightly reduce muzzle rise, but then crucify a nose heavy rifle which by its very nature does the same thing. Still though, if you’re worried about shaving off a couple hundredths off your 3 gun times, you’ll probably reach for your featherweight AR with a BattleComp 1.0 brake anyway.

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