SIG SAUER 5.56x45mm NATO Semi-Automatic SIG 556 Patrol Rifle


by Jeff Quinn

photography by Jeff Quinn & Boge Quinn

October 21st, 2010


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SIG's 556 rifle.





Ambidextrous thumb safety.



Magazine release (top), bolt release (bottom).





Folding buttstock.



Buttstock also telescopes to three positions.





Sling attachment points.







Swiss rifles have intrigued me since the days of my youth. I still have an old annual magazine on assault rifles that was put out by Peterson Publishing when Guns & Ammo magazine was at the top of their game, producing good information for readers every month. Within the pages of that “Assault Rifles” publication were a couple of Swiss fighting rifles that seemed to be the ultimate in modern small arms. However, like most things Swiss at that time, they were priced way beyond the means of a newly-married construction worker just starting out with a twenty-one percent mortgage and a baby on the way. The importation of those fine rifles into the US did not last very long, and even today the excellent Swiss SIG 550 and 551 are excellent weapons, but still priced in the US way above the competition. However, the SIG SAUER manufacturing plant in Exeter, New Hampshire is now producing rifles that are very similar to the Swiss 550 and 551. Called the SIG 556, the American-made rifle is chambered for the 5.56x45mm NATO cartridge and accepts standard AR-15 magazines.

The SIG 556 uses a very simple and robust gas piston system with a two-position gas regulator, which allows the weapon to function under adverse conditions, if necessary. The sample rifle that I tested worked perfectly with every type of ammo that I fed it in the normal position, even when filthy, so I had no cause to switch the regulator to position two, but the option is there if you need it. The 556 has an ambidextrous thumb safety that was a bit stiff to operate on the test rifle, but has a short throw and is natural to operate, pushing downward to fire. The buttstock, hand guard, and lower receiver are made from a reinforced polymer, and the three-position telescoping buttstock folds to the side for use in tight quarters or for compact storage. The SIG 556 also comes with a longer butt plate to extend the length-of-pull, if desired. The weapon will fire with the stock in either position, but only when deployed to the normal position with a drum magazine such as the Beta C-Mag. With all straight box magazines, the weapon will fire with the stock folded or extended. The trigger feel is unlike that of an AR. It is smooth with about three-eighths inch of travel, with a constant pressure throughout its travel. After getting the feel for it, it was pretty easy to use either firing offhand or for target work from the bench. The 556 has a very good set of sights. The front is a protected post, and the rear is a fully-adjustable unit with three apertures and a V-notch on a rotating drum. I first experienced a sight similar to this on an HK 91 many years ago. The design is similar, but the SIG sight is superior to the HK, in my opinion. The rear sight attaches to the integral 1913 Picatinny rail atop the upper receiver, and is easily removed to attach a scope or other optical sight. There is also a handy back-up rear sight inlaid into the Picatinny rail that flips up for use. The SIG 556 wears a relatively thin sixteen inch barrel with a one-in-seven twist to accommodate any 223 or 5.56x45mm bullet. The muzzle is threaded, with a closed-bottom birdcage AR-15 style flash suppressor attached.

The SIG 556 is very easy to disassemble for cleaning. Even after extended firing sessions, the internals of the weapon remained fairly clean, with minimal residue to remove. During rapid-fire shooting sessions, the thin barrel quickly became hot, but cooled off almost as quickly, and no point-of-impact change was noted while firing from the bench as the weapon heated.

Critical specifications are listed in the chart below. Linear measurements are listed in inches. Weight is listed in pounds. Trigger pull weight is listed in pounds of pressure. Rifling twist is listed as the length in inches of barrel to complete one 360 degree turn on the rifling. The weight on my sample gun is slightly higher than that listed on SIG’s website.

Barrel Length 16'
Barrel Diameter 0.57"
Rifling Twist 1 in 7
Gas Regulator Positions 2
Overall Length, Stock Extended 34.5" to 36.1"
Overall Length, Stock Folded 26.1"
Weight, Empty 7 lbs. 10 oz.
Buttstock Folding, Polymer
Length-of-pull 11.63" to 13.25"
Handguard Polymer
Trigger Pull 5.5 lbs.
Magazines Supplied One 30-round

For accuracy testing, I mounted my mule, the Leupold Mark 4 8.5 to 25 power target scope using an ArmaLite one-piece mount. Accuracy testing was done at 100 yards, with the results shown in the chart below. Group sizes are the average of three-shot groups at that distance. Group sizes are listed in inches. Velocity testing was done with the chronograph twelve feet from the muzzle at an elevation of 541 feet above sea level, approximately. Temperatures hovered around the eighty-two degree Fahrenheit mark during all testing. Velocity readings are the average of several shots fired, and the results are listed in the chart below. Velocity readings are listed in feet-per-second (fps). Bullet weights are listed in grains. FMJ is a full metal jacket bullet. HP is hollowpoint. ASP and FHVL are specialized bullets as loaded into ammo produced by Extreme Shock Ammunition. TSX is a Barnes Triple Shock homogenous copper hollowpoint bullet. AP is a full metal jacket bullet with a steel-tipped lead core. The handload listed uses the TSX bullet with 24.5 grains of Ramshot TAC powder, a Remington small rifle primer, and Winchester commercial .223 Remington cases.

Ammunition Bullet Weight Velocity Accuracy
American Tactical FMJ 62 2989  
Hand Load TSX 62 2799 1.50"
Winchester USA FMJ 55 2928  
Winchester USA FMJ 62 2912 1.62"
Buffalo Bore HP 69 2867 1.25"
Extreme Shock ASP 100 1187  
Extreme Shock FHVL 62 2798  
Samson FMJ 63 2812  
Black Hills HP 69 2727 1.12"
Wolf Gold HP 75 2579 1.38"
Lake City SS109 AP 62 3031 2.63"

As shown in the chart, accuracy was very good. The loads for which velocity readings are listed without accuracy data is due to not having enough of that particular ammunition available to me for thorough accuracy testing. Some of the loads tested displayed very consistent accuracy from the bench. Reliability was flawless during all phases of testing. Every cartridge fed, fired, and ejected perfectly. Case mouths were dented, and a small indentation was also noted on the body of each empty case, which might be a concern for hand loaders. However, the case mouths can be straightened by the sizing die, and the body dent is of no concern to me. Ejection was to the right and slightly forward.

The SIG 556 is a fine fighting rifle. While priced right along with the top-tier AR-15 rifles on the market, it is every bit as good, and some folks prefer this type of weapon to an AR. It is certainly a reliable, accurate weapon, and it can use any magazine that will work in an AR-15. I would love to get my hands on a select-fire version of the SIG 556, to see how this thing runs on full-auto. Judging by the recoil and handling characteristics of this semi-auto version, it will do quite well. The folks at SIG SAUER have produced a fine Swiss-designed rifle that is built in the USA, making it affordable to most of us who either cannot or will not pay the price of a good pickup truck for the Swiss version. SIG lists the MSRP of the Patrol Rifle at $2000 US, but they are selling around here for much less, making the price very competitive with other quality fighting rifles. The SIG 556 Patrol Rifle comes in a hard plastic case with one thirty-round magazine, extra thicker butt plate, and instructions.

Check out the SIG 556 and other SIG products online at

Jeff Quinn

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Click pictures for a larger version.


Excellent sights.



Flip-up rear backup sight.







The 556 comes with one 30-round AR magazine.



Accuracy testing.



Empty cases were slightly damaged upon ejection.