Sig Sauer’s 556 piston-operated carbine ready to fill many roles
by Scott Smith
Contributing Editor
A few years ago I had the opportunity to go to Sig Sauer’s Academy to attend the Defensive Rifle Course. While there I had the opportunity to shoot one of Sig’s 550 series select-fire assault rifles. The rifle was a tease because they were only available to military and law enforcement agencies; even the availability was limited. Needless to say I was left wanting; this rifle shot well, handled well, and it was just plain cool.
The staff assured me that Sig Sauer (18 Industrial Dr., Dept. GWK, Exeter, NH 03833; phone: 603-772-2302; online: sigsauer.com) was working on making the 550 family available to the public and to individual officers for purchase, but the process takes time. The plan was for Sig’s new rifle to be called the 556. It would use AR-15 magazines, keep the Sig 550 look and, to make it available to the public, it would be semi-automatic. Yet it would retain the two-position adjustable gas piston ensuring reliability under the worst of conditions.
When Sig Sauer started shipping the new Sig 556, it sold like there was a buy-one-get-one-free sale going on. This meant editorial samples of the 556 were limited, and it was nearly a year after sales to the public started that one was available for test and evaluation. Late in the Spring of ’08, a 556 arrived at my local dealer for me. Sadly the rifle had to sit and wait for me to return from school before I could shoot it.
The Sig Sauer 556 was everything I had hoped for. It is a duty-ready firearm built to accept various optics, lights, other aiming devices, and vertical forearms. It even ships with Sig’s Grip-Light. The finish of the 556 is smooth evenly applied satin black.
Unlike other “black guns” which are gas operated, the 556 is piston driven. The piston system reduces the fouling of the bolt and the associated moving parts. The gas tube vents gas through the numerous ports before the piston drives the rotating bolt. This venting is what reduces dirt, and ultimately reduces cleaning time. Should the system get dirty, the two-position adjustable gas piston of the 556 will ensure it runs in the worst of conditions.
Sig uses a 16-inch cold hammer forged barrel with one in seven twist rate to stabilize a wide variety of bullet weights. This barrel is manufactured by Sig to ensure quality control of the barrel from start to finish. Mated to the barrel is Sig’s flash suppressor, which does a superior job reducing the flash signature. The flash suppressor is an ACME type threaded to mate with select sound suppressors.
The barrel is threaded to a high carbon steel upper receiver which is Nitron® coated to ensure the receiver is corrosion resistant. This ensures a solid shooting platform capable of handling the hottest of rounds and enhancing the accuracy of the rifle. For ease of installing optics the receiver is a “flat top” Picatinny rail with a built in, hidden rear sight. This sight is not designed to be a primary sight; it is purely a back-up in the event your optics go down.
The rifle’s charging handle and bolt are contained in the upper receiver. There is no dust cover over the receiver. Sig opts to use a slotted rubber cover to keep debris out of the receiver. This system seems to work well, since I haven’t noticed any “stuff” in the receiver.
The upper receiver is mated to the lower using a rear push pin and slotted front pivot pin. There is no play between the receivers; and the seam is flush and smooth.
Like many other black guns, the lower receiver is CNC machined aluminum which is hard coat anodized. The ambidextrous safety and magazine release are located on the lower receiver as they are on an AR-15. The bolt release is behind the magazine well above the trigger and is pushed down to lock the bolt or up to release it.
A major design change for the 556 over other 550 series rifles is the magazine. Sigs have used proprietary magazines which are in limited supply. Sig redesigned the 556 to accept AR-15 magazines giving operators a large and affordable supply of magazines. The mag well on the 556 is larger than those on ARs, assisting in smoother, faster reloads.
The forearm is a vented aluminum quad rail. Venting the front rail reduces heat build up and reduces weight of the 556. To protect the Picatinny rails, Sig includes snap-on polymer rail covers. The railed forearm and receiver are level, allowing optics to mate with magnifiers and night vision devices.
Sig ships the SWAT 556 with Sig Sauer’s Grip-Light. This is a vertical grip with removable high intensity LED light, STL 100. There is a trigger to activate the light and it can be locked out so you don’t inadvertently activate the light when not required.
While the 556 doesn’t use a buffer tube assembly common to ARs, the 556 was designed to accept AR stocks. Sig Sauer installs Magpul’s (PO Box 17697, Dept GWK, Longmont, CO 80308; phone: 303-828-3460; online: Magpul.com) CTR, an adjustable five-position stock on this carbine. The CTR is an adjustable stock that can be locked in place, which reduces the chances of the stock accidentally collapsing and it eliminates the wobble of adjustable stocks.
The Sig Sauer 556 was finished in all black with Sig Sauer’s Nitron® finish or hard anodizing. Both finishes were smooth and even on all parts. The finish on the 556 will help ensure your carbine does not corrode and is easily cleaned.
Before I took the 556 to the range I did make a few changes/additions. The first change I made was to remove the Grip Light and install a Wilcox Industry’s (25 Piscataqua Dr., Dept GWK, Newington, NH 03801; phone: 603-431-1331; online: wilcoxind.com) Steady Grip with bi-pod. This grip gives you a quickly deployable bi-pod and adds very little weight to the carbine. This bi-pod is very stable and is what I planned to shoot the 556 from when testing its accuracy.
Having previously fired Sig’s 550 series, I knew the rifles are accurate right out of the box. This meant the 556 required optics that could function for multiple missions. For this reason I chose Leupold’s (14400 NW Greenbrier Pkwy., Dept GWK, Beaverton, OR 97006; phone: 800-538-7653; online: Leupold.com) Mark IV CQ/T. The CQ/T is variable power scope with a magnification range 1-3 power. This scope gives you a dot for fast acquisitions at close quarter battle distances while giving you magnification when accuracy is required. The CQ/T also gives you an electronic amber dot for low light applications. Best of all, this dot is powered by easy-to-find AA batteries.
To mount the CQ/T, I chose to use ARMS Inc.’s #12 mount. This mount allows you to rapidly remove the CQ/T to use the back up sights or to install a more powerful telescopic sight should you need to make a more precise shot. The ARMS mount is rock solid and does not require you to confirm your sights zero when you replace it.
Last I contacted Magpul to acquire the rubber butt pad and cheek riser for the CTR Stock. The riser ensures proper eye to scope alignment and the rubber butt pad reduces the slipping of the stock during sustained firing. These two items were purely personal choice and not required to make the 556 run.
Now that the Sig was equipped with optics it was time to take it to the range and see what the rifle could do. I had a mixed bag of .223 Rem. ammunition that I used to zero the CQ/T because I didn’t want to burn through premium ammunition getting the scope on paper. I know that many folks will disagree with this but from past experience I have found if you get on paper with generic .223; it requires much less good ammo to tweak “0”.
Once I had the 556 zeroed I loaded the magazines with 60-grain loads from Hornady (3625 Old Potash Hwy, Dept GWK, Grand Island, NE 68802, Phone: 308-382-1390; online: Hornady.com) TAP FPD and Black Hills (PO Box 3090, Dept GWK, Rapid City, SD 57709; phone: 605-348-5150; online: black-hills.com) V-Max. These loads have proven to be accurate in my other .223 Rem. chambered rifles; I figured the 556 would follow suit.
I was not let down as the Sig shot both loads well. I fired 10-shot groups of both loads at 100 yards off the Wilcox Steady Grip/Bi-pod. The Hornady TAP FPD barely edged out the Black Hills V-Max by a 1/16th of an inch. Both loads clover leafed several rounds but it was a balmy 12 degrees when I was shooting so the operator may have shivered the group out to 1.25 inches. I am certain on a more climatically agreeable day; sub-MOA groups with the Sig Sauer 556 with Hornady TAP and Black Hills V-Max 60 grain loads. This rifle is simply that accurate.
For grins I loaded the 556 with 52-grain Black Hills Match Hollow Points; remanufactured. I did not adjust zero, simply sighted in and let fly. At one hundred yards the 556 kept ten round groups at less than two inches, about an inch high from point of aim.
Knowing how well Sig Sauer rifles shoot, I also wanted to mount serious optics for use at longer ranges on the rifle. For this I chose a Vortex (2120 West Greenview Dr., Middleton, WI 53562; phone: 800-426-0048; online: vortexoptics.com) Viper Riflescope. This scope is a 4-12X 40 scope with parallax adjustment. I mounted the Viper with LaRue Tactical’s (850 County Rd. 177, Dept GWK, Leander, TX 78641; phone: 512-259-1585; online: laruetactical.com) LT-123 two piece mount/base and LT-136 inserts to convert 30mm rings to one inch. The Vortex Viper is one of the finest scopes I have used and topping the Sig 556 with it should make this rifle wicked accurate at intermediate distances of 200 to 400 meters.
Since this rifle shot well with Leupold’s CQ/T mounted, I suspected with the Vortex Viper mounted that the Sig Sauer 556 would be a tack driver. I again zeroed the scope with mixed fodder and the Sig was soon shooting under an inch using this collection of ammunition. When I dialed it in using Black Hills and Hornady 62-grain ammunition, the 556 was shooting one hole 5-shot groups at 100 yards. At 200 yards the group opened up to just over a ˚-∫ inch. Needless to say it was substantially warmer when I was shooting the 556 with the Viper mounted than when I was shooting it with the CQ/T. This coupling of a fine Sig Sauer 556, quality ammunition from Black Hills or Hornady, and Vortex’s Viper makes for a wickedly accurate precision rifle package.
While ringing out the Sig Sauer 556 and the Viper combination, I used a few loads of ammunition from a couple of smaller ammunition companies. The first is BVAC-Bitterroot Valley Ammunition Company (5348 Florence-Carrolton Loop, Dept GWK, Florence, MT 59833; phone: 406-273-9140; online: bvac-ammo.com) and Atlanta Arms and Ammunition (721 Vine Circle Social Circle, Dept GWK, GA 30025; phone: 770-464-2203; online: atlantaarmsandammo.com). BVAC is known for the hunting ammunition they produce and from what I saw of the 64-grain soft point and 75-grain tactical load, BVAC will be known for making fine ammunition for competition and duty use. The ammunition quality rivaled that of the “big” name producers. The 556 produced sub 2-inch groups at 200 yards with both BVAC offerings.
Atlanta Arms and Ammunition is well known in action pistol circles. Atlanta Arms supplies such unknowns as Team Glock and the Army Marksmanship Unit (AMU) with their match ammunition and these teams have won a few matches over the years. The 60-grain V-Max I ran through the Sig was remanufactured and I will challenge anyone to show me the difference from factory new. I also used a load Atlanta Arms supplies to the AMU, 77-grain HPBT. This round was very accurate out of the 556, shooting sub-1˚-inch groups at 200 yards.
Atlanta Arms and BVAC offer shooters ammunition that performs well, is consistent, match grade accurate and you get to talk to the boss if you have issues. Try to do that with many of the brands that populate the shelves of the big box stores. If you are looking for ammunition, check these two smaller, less well known operations out; they make quality ammunition.
I would feel comfortable using the 556 with the CQ/T for duty or three-gun competitions or I can swap out optics to the Vortex and have a rifle for precision applications be it counter-sniper to eradicating the local varmint population. This is truly a multi-purpose rifle and will serve the owner for years to come.
When you couple quality ammunition and the Sig 556, the Leupold Mark VI CQ/T and the Viper Vortex, you have a versatile weapons system. I was so impressed with the 556 and CQ/T or Viper, I have permanently added them to my vault. Since I planned to keep this rifle I made a few additions. First, a front clamp Sling Thing from GG&G (3602 E. 42nd Stravenue, Dept GWK, Tucson, AZ 85713; phone: 800-380-2540; online: gggaz.com) with its quick detach sling loop, a Spec Ops Brand (PO Box 475, Dept GWK, Monahans, TX 79756; phone: 432-943-4888; online: specopsbrand.com) Mamba Sling and I applied Lauer’s (3601 129th St., Dept GWK, Chippewa Falls, WI 54729; phone: 715-720-2950; online: lauerweaponry.com) Duracoat to it in ABU camo.
The Sling Thing is a rock solid mount for its pivoting sling swivel. When coupled with the sling swivel on the CRT and Spec Ops Brand’s Mamba, the 556 lays flat on your chest, allowing access to your back-up sidearm, applying handcuffs, or anything else you need two hands for.
I coated the Sig Sauer 556-CQ/T with Dura Coat because I wanted my rifle to be unique, plus it makes the weapon easier to clean. Coating the rifle in a camouflage pattern also allows the rifle to blend into its environment; basic black stands out in a desert or brush setting. This finish also makes the carbine’s system more corrosion resistant. For duty, being able to clean the carbine and protecting it from the elements are both major pluses.
For truly precision work I wanted to add a Harris Bi-pod (Harris Engineering, Inc., 999 Broadway, Dept GWK, Barlow, KY, 42024; phone: 270-334-3633; online: harrisbipod.com). To do this I needed a mount, so I contacted Brownell’s (220 S. Front St., Dept GWK, Montezuma, IA 50171; phone: 641-623-5401) for an adaptor. The adaptor uses three set screws to secure the base to the 556’s Picatinny rail. This is rock solid and will serve you for years to come. I mounted the adaptor and Harris to the 556 and it was as solid as any solid stock or precision stock on a bolt-action rifle
What is my opinion of the Sig Sauer 556? As I previously stated, I added it to my vault; I purchased it. With this rifle’s accuracy it can be used for competition or varmint population control. Simply put: the Sig Sauer 556 is a fine tool.
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