The SIG556 Classic Patrol & SIG516 Patrol

John Morrison




Our sample SIGs: The SIG556 Classic Patrol at top, and below, the SIG516.

When these guns arrived, they were still prototypes. In today’s market, firearms manufacturers have been known to push designs out the door before they’re really ready, in effect, doing their “beta testing” on serious end users. I could only hope SIG hadn’t done that. To me, they were unproven, and there was the possibility I’d have to tell SIG and our editor, “Nice tries, but no cigar; they suck.”

The bottom line: By the time testing was complete, SIG556 Classic Patrol’s were in production, so they let me buy the test sample. It’s now my number-one truck and closet carbine. The SIG516 prototype had to be returned to SIG, but I immediately placed an order for one, and I’m selling two other AR’s to pay for it. That’s a solid endorsement by a demanding user.




With a protected front sight mounted on the gas block and SIG’s RDSS rear diopter sight included, the 556 Classic Patrol is ready to rock — right out of the box.

The 556 Classic Patrol was accompanied by a standard 556 owner’s manual, and I quickly found there were changes in addition to the “shorter and lighter” features. The bolt handle, formerly angled upward, has been straightened so it projects straight out at 90 degrees. The previous angle made it easier for users to reach over the receiver with their left hand and operate the bolt. That dated from the days before placement of a 12 o’clock receiver rail. Presuming users will mount optics, that becomes a non-issue and the new angle is easier to use. Also, the forward pin connecting the upper and lower receivers used to be a two-piece threaded design; it’s now user-friendlier with a  captive push-out pin.




SIG556 “standard” gas system is at top; shortened Classic Patrol system is below it. Note the simple, robust design.

The big change, of course, is the shortened gas system. As stated in the print article, shortening a gas system can have catastrophic results. Changes in gas volume and pressure; heat, bolt velocity and critical timing issues can destroy reliability, particularly in extraction and ejection. But few makers have anywhere near the experience with piston systems that SIG does. The SIG556 Classic Patrol is a direct descendant of one of the most respected battle rifles in history — the Swiss Army-issued SG 510 or Sturmgewehr 57 — and its heart and guts carry DNA from the current-issue SIG SG550/Stgw 90. SIG got it right.

I mentioned, “cool running” in the article. In early 2010, an independent testing outfit used sensors, which gauged heat at the bolt, chamber and barrel. They tested two gas-piston AR’s, a direct gas impingement (DGI) AR, and a SIG556 after firing thirty rounds. The SIG556 ran coolest at all three points. I don’t have sensors, but it appears the Classic Patrol has inherited that cool-running trait.




Upper and lower handguards of a “standard” SIG556 at top; SIG556 Classic Patrol at bottom.

Here’s another place where weight was saved: The handguards of the “standard” SIG556 weigh 14.0 ounces, versus the Classic Patrol handguards’ weight of 5.2 ounces. That’s nearly half a pound right there. The standard handguards are of course longer to cover its longer gas system, but also thicker and heavier in order to better stabilize the molded-in 1913 rails. I’ll give up the rails for the faster, more agile handling of the Classic Patrol. I would suggest if you need more rail-space for accessories, look at Warne Tactical’s RAMP optics mount, which provides a short, angled rail-mount on either side of the main 12 o’clock mount. See it at




Here’s the Classic Patrol’s two-position gas valve. When the plug is oriented straight up and down, it’s in “normal” mode. Simply depress the detent pin and turn the plug to position two if the action becomes sluggish. It didn’t. Note: Do NOT shoot with the gas valve in position two if it’s not indicated; you’ll just introduce unnecessary force to the action.




The Classic Patrol’s Swiss-style stock easily folds to the right with a press on the left side of the hinge, and snaps in securely. Just give it a brisk tug to release and swing it back to automatically lock in the extended position. Note that you don’t have clear access to the magazine release when the stock is folded. This stock provides a good cheek weld.




Here’s the RDSS — SIG’s Rotary Diopter Sight System. The style is unfamiliar to Americans, but it’s a rugged, combat-proven design capable of surprising accuracy — with the exception of the gross close-quarters V-notch discussed in the print copy. And it’s a lot faster and easier to use than other types of adjustable iron sights. Try using the 100-meter aperture for zero-to-100-plus.




If you buy a SIG556 Classic Patrol of your own, consider using Mil-Comm cleaner, grease and lubricants/protectants; SIG SAUER does.

The Classic Patrol came liberally treated with Mil-Comm TW25B lube and light grease — in my opinion, too much for shooting, but fine for shipping purposes, because they never know how long shipped stock will be stored and under what conditions. All I did was wipe off the excess, ran a patch down the bore, and that was it for over 700 rounds in testing, then over 400 after that. There was no unusual fouling or carbon buildup.

During initial testing, winter made a cameo reappearance with wet, heavy snow and some sleet. I considered the weather a valid part of the test, and made no attempt to shelter the carbine; just shook it off and kept shooting. I didn’t even wipe down the exterior. During the last few days of shooting, it was exposed to warm, dry conditions with blowing dust and grit from fresh excavation at the range. I left it benched frequently with no mag in the well and the receiver open. At the end of testing, she still ran slick. Performance of the lube and grease was excellent. Based on that, I’ll continue using Mil-Comm products on the 556.




The tan case seen in photos is the BLACKHAWK! 40-inch Homeland Security Discreet Weapons Carry Case — an outstanding piece of gear with lots of features; removable closed-cell foam lining, multiple mount points for the included shoulder strap, weapon-securing straps in the main compartment, and a broad band of loop-pile material holding a panel of three magazine pouches inside the side compartment. I learned the SIG516 could be carried in the main compartment, and the SIG556, with stock folded, fit neatly into the 35-inch side compartment. The sling shown is a BLACKHAWK! Dieter CQD Sling; fully adjustable and equipped with heavy-duty snap hooks, it worked very well on the SIG556. There’s just enough stretch in the bungee sections to allow some flex and dexterity for position changes and close-in impact-fighting, but not too much. The elastic end covers push up over the snap hooks to quiet them down, too.




Inherent accuracy testing on the SIG556 was done using the Pride-Fowler Rapid Reticle 1-4x24CQLR Illuminated Reticle scope. I won’t go into a lot of detail on it, because (a) there are lots of details, though it’s easy to use; (b) it is, in my opinion, less appropriate for a patrol carbine and more appropriately placed on a patrol bolt rifle or a SWAT-dedicated perimeter-containment or site-coverage precision carbine; (c) because I’ll write it up in detail in a future issue. In brief, this optic almost “stole the show” during testing. It’s a superb headhunting scope. Check it out at The mount is another winner: a LaRue Tactical QD LT104. Rugged, exact and repeatable, their advertising claims it’s “…the best mount made for attaching high-power riflescopes onto flattop-style AR15’s, period” — and they might be right.

But Wait, There’s More!




The SIG516 with SIG’s STS-081 red dot sight.

Note the Urban E.R.T. Sling equipped with QD swivels plugged into the machined-in QD sockets. It was received halfway through testing, and quickly proved to be one of the best, most comfortable, secure and versatile slings available. Check it out at You’ll be hearing more about it in the future. The ACU-camo case is the 36-inch Assault Systems Rifle Case by Elite Survival Systems, and it’s everything a rifle case should be — well-padded, tough, and it features five magazine pouches plus extra space for tools and ammo.




See the spring-loaded plunger in the recess? This goes a long way toward making the SIG516 a lifetime investment. This exerts constant pressure between the upper and lower receiver, holding both in alignment, reducing or eliminating the movement, rattle and shake often found in even well-made new AR’s, and becoming pronounced in well-used ones. I’ve seen a half-dozen drop-in fixtures designed to address this, but none built-in like this; just another example of SIG seeing a problem that’s been around for fifty-plus years and fixing it without fanfare.


SIG 10


The SIG516’s gas valve has three positions: one for “normal” conditions, one for dirty/fouled conditions, and one for use with suppressors. An optional fourth position would negate reciprocating action movement for single-shot use with a suppressor. Just depress the stop pin and twist. You can insert the nose of a cartridge or other object through the hole in the gas plug for more turning leverage if necessary.


SIG 11


The 516’s gas pushrod system is strong, simple and includes no tiny loose springs, cones or couplers just waiting to leap out and get lost. It’s easily disassembled and cleaned.


SIG 12


Here’s the bolt and carrier of the 516. Note the carrier has an integral impact face for the gas pushrod rather than a staked gas key, which could shoot loose. It’s an anti-tilt design and further relieved for clearing liquids, mud or sand if it — and you — wind up in the soup.


SIG 13


Check the left-side half of the 516’s ambidextrous mag release, the thicker-than-normal stout mag well lips and nicely angled mag well funnel. You can just make out the vertical grooves on the front face of the mag well, which provide better grip if you “choke up” with your off-hand. SIG really did their homework on this puppy.


SIG 14


As opposed to the 556 Classic Patrol, the SIG516 arrived dry as a bone. I was tempted to treat it with the best single-purpose products I had, but then thought, most LE agencies provide, at best, just an all-purpose lube/cleaner/protectant — particularly when it’s for general-issue patrol weapons. I had just received a pump-can of Centerfire’s biodegradable WeaponCLP and the recommendation of an LE armorer acquaintance. I disassembled the 516, wiped it down inside and out very sparingly with WeaponCLP and ran it hard. After initial testing, I purposely subjected it to more blowing dust and grit. The WeaponCLP performed very well, and did not show any tendency to gum up.


SIG 15


The SIG516 ships without backup iron sights (BUIS). There are lots of good ones out there from MagPul, Troy Industries and others, but none faster or better made than these from Diamondhead Sights. Just visualize the ease and speed of lining up these sights and you’ll start to get the picture. The geometry of the design is so intuitively self-centering and aligning it’s nothing short of amazing — the fastest iron sights I’ve ever used. They’re also absolutely top-quality in materials and precision machining. They fold down neatly, flip up and lock solid when deployed. Check them out at While you’re there, look at their new Auto-Ranger sight. I haven’t used one yet, but the concept looks very interesting.


SIG 16


Left to right, magazines used in testing included SIG SAUER-marked polymer mags, MagPul MagLevel P-Mags, Brownells’ military-contract mags, Israeli-made Count-Down Mags distributed in the US by EMA Tactical, a Fusil-USA MIG-welded steel mag, and a vintage Colt military mag. All functioned perfectly, except for one previously damaged Colt mag which snuck into the range bag. Neither the 556 nor the 516 showed any preference or “stickiness” with any of them, and none were loose at any point. This speaks well for the dimensional precision of both weapons, because often you’ll find if a carbine will “eat any flavor magazine,” it will rattle-and-drop some, while other guns may hold most mags tight, but be too tight and sticky with others.


SIG 17


Note the MagLevel P-Mag and Count-Down Mag both offer visual confirmation of your rounds remaining — a handy feature.


SIG 18


f all the ammo used, it came as no surprise that generally, heavier rounds proved to be the most accurate in these 1-to-7-inch rifled barrels. The standouts were Black Hills 77-grain and Cor-Bon 69-grain HPBT. However, loads down to the 52-grain Black Hills Match HP and Cor-Bon’s 53-grain DPX also performed with great precision. American Tactical 62-grain 5.56x45mm rounds, made in Turkey, turned in very good performance, as did the Serbian-made PRVI Partisan 62-grain ammo. Both of them are good low-cost training and practice alternatives to premium duty ammo.

Next time out, I want to test Pakistani reloads in a carbine made by “Bill & Earl’s Lawn Chairs & Fine Firearms” just so I’ll have something substantive to complain about! – Morrison


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