Time to Run the Gun
In preparation for testing, I lubricated the 556 thoroughly, grabbed a 3X Trijicon ACOG with an integral mount and headed to the range with a variety of ammo.

The two-position gas valve, located just below the front sight, allows the user to adjust the amount of gas flowing against the operating rod. The vertical position is for normal use. When the gun gets gritty, turning it to the second position allows more gas to push against the rod to ensure reliable operation.

I first checked the iron-sight zero at the 25-yard line. At first glance, the rear aperture looks pretty darn small, but it works very well. The sights provided an excellent sight picture and were almost dead-on with 55-grain ball.

Before mounting the ACOG, I loaded a bunch of Magpul’s P Mags with Winchester’s 55-grain FMJ ammo and ran them through the carbine at warp speed. The carbine ran reliably and was noticeably cooler than a conventional AR-style, direct-gas-impingement gun. It was also easy to control, due in part, no doubt, to its excellent trigger. Although the two-stage affair broke at more than seven pounds on my trigger-pull gauge, the second stage was closer to three pounds and very crisp.

To say empties were ejected smartly is an understatement—the 556 ejected expended hulls with enough force to do some serious damage to anyone foolish enough to stand in the way. My friend police firearms instructor Lance Bertolino commented that he had never seen a firearm shuck empties so forcefully. We both found it much more amusing than did the hapless guy sitting two benches down.

After checking the iron sights, I installed the Trijicon for accuracy testing. It went on easily with the integral mount, but the knobs interfered with the charging handle. I didn’t have the tools to reverse the scope on the mount, so I had to move the ACOG all the way to the last slot to allow enough room for the charging handle to go all the way back.

ACCURACY RESULTS:
LOAD	BULLET WEIGHT (gr.)	CLAIMED VELOCITY (fps)	AVERAGE ACCURACY (in.)
Federal Match	69	2,950	1.1
Hornady TAP	75	2,790	1.95
Winchester BST	55	3,240	1.95
Time constraints prohibited chronographing. All velocity figures are factory claimed. Accuracy results are the average of five three-shot groups at 100 yards using a Caldwell rifle rest and rear bag.

Since the 556 has a 1:7 twist, I began my 100-yard shooting with the heaviest load I had on hand, Hornady’s 75-grain TAP round. I must confess that shooting tiny groups with a 3X scope and a large, inverted-triangle reticle designed for ventilating bad guys instead of paper was no easy task. In fact, I blew several groups that would have classified as screamers had I not choked on the third round. But I still managed to post some pretty impressive targets considering the limitations of the optic and the fact that I was firing a semiautomatic carbine with a pencil-thin, 161?4-inch barrel.

As evidenced by the included accuracy table, the 556 SWAT was pretty darn accurate with all three of the test loads. It exhibited a clear preference for heavier bullets, but that was to be expected with its quick twist rate. Still, it shot less than two inches with the 55-grain Winchester load, which is more accurate than some carbines’ “best” groups.

The Last Word
I would like to have had more time with the 556, but I shot it enough to see that it is an accurate, reliable carbine. Given its lineage, I was not surprised, but it was nice to see that modifying the classic 550-series design didn’t diminish its legendary Kalashnikov-based reliability one iota. The one-pound weight loss, however, greatly improved the 556’s handling qualities.

I was enamored with the 556’s fine trigger and greatly impressed with its overall fit and finish. The controls were easy to use and intuitively located, and the bolt hold-open on the last shot was a nice feature that is lacking in all too many European designs. And I must confess that I didn’t miss the springy twang of the AR-style buffer tube one bit.

If there is a knock on the 556, it is that it’s awfully tight. While that quality contributes to the carbine’s accuracy and solid feel, those tolerances can work against the gun in harsh battlefield conditions. It would make a fine patrol rifle or home-defense piece, but I don’t think we’ll see any private contractors buying the 556 for a desert deployment.

The author’s accuracy tests were made easier by the 556 SWAT’s fine trigger. The best group was this .786-inch cluster using Federal’s 69-grain Match ammo. Photos by the author

That being said, I think SIG Sauer will be fighting 556 backorders for some time. After all, tactical rifles and carbines have never been more popular, and SIG’s legendary accuracy and reliability combined with the 556’s acceptance of abundant, affordable, mil-spec AR-15 magazines pretty much guarantees it success.

The 556 SWAT comes with a SIG tactical light. Its flip-up sights are clearly visible here. They are not, in the author’s opinion, as nice as the 550 series’ diopter sights, but they are much smaller and lighter and they get the job done.