Recognizing a strong demand for a variant of the Swiss SIG SG 550 series of rifles in 5.56x45 mm NATO, SIG Sauer—the U.S. subsidiary of SIGARMS in Switzerland—developed a semi-automatic variant manufactured here in the United States. This rifle, the SIG556 in .223 Rem., combined elements of both the original 550 series and the highly popular AR-pattern rifle.
While the SIG556 shared many primary design features with its Swiss cousin, such as a long-stroke gas piston system of operation, a pressed-steel upper receiver assembly, and similar overall configuration and operation, it did differ in some significant ways.
One of the most noteworthy of these was the use of a lower receiver (dubbed the trigger casing by SIG Sauer) manufactured from 7075-T6 forged aluminum alloy rather than pressed steel, reducing the SIG556’s comparable weight by roughly one pound. In addition, the lower receiver also employed AR-15/M16 magazines.
Additional changes included an AR-pattern collapsible stock and redesigned fore-end that incorporated strips of Picatinny rail. The result was a rifle that, while still capturing the overall charm of the original SIG series, was aesthetically quite different. SIG Sauer recognized some consumers want a variant styled more like its Swiss cousin. The company’s answer is the SIG556 Classic.
Although from a mechanical standpoint the SIG556 Classic and the standard SIG556 are practically the same rifle, aesthetically and ergonomically the two variants are quite different. Primary changes to the Classic over the standard rifle center around the sighting system, the stock assembly and the fore-end.
Whereas the standard SIG556 featured a simple open post front sight, the Classic has a heavy-duty winged post front sight assembly similar to that of the 550 series. The Classic shares the standard SIG556’s Picatinny rail-equipped upper receiver with a built-in folding emergency sight, but SIG Sauer also offers an optional heavy-duty steel diopter rear sight that is very similar to that of the original 550 that attaches to the Picatinny rail.
Rather than a collapsible AR-style stock, the Classic sports a Swiss-style triangular-shaped polymer stock assembly that can both fold alongside the receiver as well as be adjusted to three lengths of pull. To fold the stock, the shooter simply presses a half-moon-shaped release button on the forward left side of the stock.
Length-of-pull adjustments to the stock are made by pressing in on a large integral lever on the belly of buttstock and adjusting the stock out to any one of the three preset lengths. The total range of adjustment is 1 1/2 inches, in three 1/2-inch increments. In addition, SIG Sauer also includes three interchangeable internal plates that allow users to set the stock to adjust to either preset lengths or leave it fully adjustable. A secondary buttpad with an additional 1-inch of length is also included.
The Classic’s polymer two-piece fore-end, like the buttstock, is also styled much more like that of the original Swiss design, featuring a streamlined shape with molded-in ribs and integral cooling vents. The fore-end is also drilled to accept three optional strips of polymer Picatinny rail. The lower handguard features a protrusion on its rear right side that interfaces with a latch on the buttstock to retain it in its folded position. To engage the latch, the stock must be fully extended when folded.
In terms of function, the SIG556 Classic has a rotating bolt and a gas piston system of operation. The gas system is adjustable with two settings—“standard” for normal operation and “emergency” to allow more gas through when needed. Adjustments are made by twisting the gas valve located on the forward face of the front sight base assembly. The 17-inch barrel of the rifle is topped off with a birdcage AR-style muzzle brake.
The rifle we received for testing came packed in a hard plastic case with a single polymer SIG Sauer 30-round magazine and a SIG Sauer-branded 1X mini red-dot sight. Also included with the rifle was the optional steel diopter rear sight unit. The SIG Sauer magazines are designed so that multiple magazines can be attached together with a synthetic coupler by way of the molded-in rails on their sides.
The fit and finish of the SIG556 Classic was excellent, with an evenly applied manganese phosphated finish on the steel parts and an anodized finish on the aluminum lower. All controls functioned positively, and the stock was easy to both fold and extend, locking solidly in both the open and closed positions.
We took the Classic out with a selection of Black Hills, Federal and Winchester .223 Rem. ammunition. During the course of a few hundred rounds there was not a single malfunction. Accuracy was quite good considering that we only used the 1X optic and iron sights. We did note a tendency for barrel heat to affect accuracy. We also noted the extremely soft recoil impulse of the SIG556 Classic, more akin to a gentle push than a sharp blow.
For those looking for the European cachet of the Swiss SIG SG 550 series rifles without the extreme sticker shock of an original, the new SIG556 Classic from SIG Sauer should make for an excellent choice.