A few years ago I had the opportunity to attend SIG Sauer's Academy and take the Defensive Rifle Course. While there I had the opportunity to shoot one of SIG's 550 series select fire assault rifles. I loved that weapon and I wanted one. Unfortunately, they were only available to military and law enforcement agencies, so my desire to own one went unfulfilled.
But the staff assured me that SIG was working on making the 550 family available to the public and to individual officers for purchase. 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. Best of all, it would retain the two-position gas adjustable gas piston, ensuring reliability under the worst of conditions.
When SIG started marketing the 556, it sold like there was a buy-one-get-one-free sale on the things. 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. Ever since it arrived months ago for testing, I've been putting the 556 SWAT SIG through its paces. The rifle has been everything I hoped for.
The 556 is a duty-ready rifle built to accept various optics, lights, other aiming devices, and vertical forearms; it even ships with SIG's Grip-Light.
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 ensures that it will run in the worst of conditions.
SIG uses a 16-inch cold hammer forged barrel with one-in-seven twist rate on the 556 to stabilize a wide variety of bullet weights. As an added bonus, the company makes its own barrels, so it can maintain quality control throughout the manufacturing process. Mated to the barrel is SIG's flash suppressor, which does a superior job reducing the flash signature of the 556. The flash suppressor has an ACME-type thread, so it will 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 rounds while enhancing the accuracy of the rifle. To facilitate the installation of 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 backup 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 out debris. It appears to me that the system works well. I say this because I haven't noticed any "stuff" in my 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.
As on many other black guns, the lower receiver of the 556 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 up to release it.