The Sig Sauer 556 Classic SWAT rifle was Sig Sauers attempt at bringing an updated version of the Sig 550 series of rifles to the North American shooting market. Like the Sig 550, the Sig Sauer 556 never gained traction, It wasn’t a mistake on Sig’s part so much it just was a rifle that was lost in a sea of cheaper rifles. The AR-15 had been for the most part standardized long ago and was considerably cheaper than the Sig Sauer 556. In the whirlwind of the anti gun movement at the time the rifle was released its easy to tell why consumers chose to spend their money in rifles they knew like the AR-15 rather than new rifles they might not have known much about like the Sig Sauers 556 Classic SWAT. I have been intrigued by the Sig family of rifles for years so when I had a chance to acquire a Sig Sauers 556 Classic SWAT that had a very low round count, I had to grab the opportunity and take a risk.

If i had to describe the Sig 556 Classic SWAT I would say its the best parts of the AR-15 mated with the AK-47 with a dash of Swiss style and quality control added to it. The rifle takes the standard AR-15 magazine and fires the 5.56 x45 cartridge but essentially uses an AK-47 type of gas system that is adjustable. It’s an appealing idea for sure, something that uses magazines that most gun owners that read this site have, firing a round that is available just about everywhere, but isn’t the standard boring old AR-15 that we all own. We figured that since some of our readers may not know about the Sig 556 family of rifles we would make a list of what about the Sig 556 is similar to the AR-15 we all know and love, and what is different about it.

What’s Similar to the AR-15 ?

  • Barrel length
  • Uses standard AR-15 magazines
  • Magazine release and location in same spot at as AR-15
  • 5.56 NATO chambering
  • 1:7 twist rate

What’s Different ?

  • Different trigger
  • Stamped Steel vs Aluminum upper receiver
  • Different bolt
  • Different recoil system
  • bolt release operates slightly differently
Authors Photo

Breakdown and Operation

Now that I have the luxury of owning a Sig 556 rifle I am amazed at how easy it is to become familiar with, being a current AR-15 and AK47 owner its a very natural transition to the Sig 556. The receiver breaks down like an AR-15 using two push pins to separate the upper and lower halves of the gun, the bolt however is a bit different. The rifle lacks an AR-15 style charging handle, instead it has one on the bolt similar to the AK-47, but with a twist. The bolt handle is removable to allow the bolt to slide out the rear of the rifle, again like the AR-15. Like I said in the beginning this rifle is a hybrid of both designs.

Once the bolt slid out of the upper receiver it was like I was looking at a slightly modified AK-47 bolt carrier group. In the image below you can clearly see the pronounced angled ramp on the rear of the bolt and the rotating head and locking lugs on the bolt itself. When you hold the two bolt side by side it becomes obvious. One of the major differences between the two bolts though is that the AK-47 pattern bolt is set up to accept a recoil spring from the rear and the Sig 556 bolt uses a piston system and the recoil assembly meets the carrier just above the bolt. The lever shown n the Sig bolt is what you depress to remove the charging handle.

Authors Photo

Different Style of  Trigger 

The trigger on the Sig Sauer 556 Classic SWAT isn’t like any other trigger I have come in contact with. When we think of triggers on rifles we think of a time tested hinged trigger, where the trigger pivots on a shaft or trigger pin, this isn’t the case with the Sig Sauer 556 rifle. In the Sig rifle the trigger rotates back and comes into contact with a plunger type assemble, this assembly then releases the hammer. This system does have some drawbacks but they are easily overcome with practice. The trigger has a moderate amount of travel that will very very different from what traditional AR-15 owners may experience, this take up in the trigger just makes it feel very long but has slight resistance. The truly interesting part of the trigger is when it engages the plunger assembly. Once the trigger has traveled this far you feel some resistance then the trigger breaks very smoothly. It’s a hard feeling to describe but there doesn’t feel to be a hard shelf that the trigger has to break over. It’s just an even push and then it breaks. I am curious to see how this will feel during live fire sessions, for now I just keep cycling the rifle and find that the trigger is like nothing I’ve ever shot. If I had to describe it I would say its long like an MP5 but much better. In the below image you can see the plunger.

Authors Photo

Other Features

One of the final features on the Sig Sauers 556 Classic SWAT that intrigued me was the two position gas piston system and how it operates. According to the Sig Sauer manual if a shooter is running into ejection and feeding problems due to heavy fouling they can move the gas valve to a higher setting. This higher setting allows more gas into the pistol assembly to help in ejecting spent shells and helping to ensure the rifles doesn’t jam. My initial thoughts on this were that given the wide range of .223/5.56 mm ammunition on the market and how some if it tends to be on the lower end of the pressure scale, that this might be an effective way to be able to shoot the worlds cheapest ammo such as Wolf without having cycling problems.

The gas system dissembles by simply pushing a detent and rotating the assembly 1/4 turn and removing it from the muzzle end of the rifles upper receiver. It’s really simple, but for some reason I expected something more complex given the rifles European heritage. When reassembling the gas system the engineers are Sig Sauers made it incredibly easy and almost impossible to mess up.

I almost forgot that the Sig 556 Classic Swat also comes with a side folding stock available in two configurations. The most sought after is the non adjustable “Swiss Style” stock that mine features. The other available stock is a side folder that also is collapsable similar to the common AR-15 stock. There are available adapters that allow a user to install an M4 style tube and mil spec AR-15 stock.

Authors Image: Adjustable gas block shown in the “Dirty” position

While the Sig Sauer 556 Classic SWAT is a forgotten rifle that Sig Sauer doesn’t produce anymore it didn’t dampen the appeal for me. This rifle is not the Sig Sauer 556 Xi that was released a few years ago, although more than once it was confused with it or its inspiration the Sig Sauers 550 rifle. Those rifles are separate lines than this rifle. To add more confusion Sig refers to their Piston Drive AR-15 as the model 556 sometimes. You would think for a company that prides it’s self on paying such close attention to detail that they could figure out an easier numbering system.

The plan for this rifle is for me to put either a Sig Sauer Romeo 7 or the new Nikon 1x-4x BLACKFORCE 1000 scope on this rifle and run at least 1,000 rounds through it in the near future. This wont be a toss in the mud and drag it behind a truck test, it will just be a simple series of tests with several different shooters to test its durability and accuracy. There are some guns that I would perform a torture test on, but that’s not happening to this rifle, I know this will disappoint some readers. We hope you enjoyed this look at the Sig Sauer 556 Classic SWAT, look for the range review in the near future. We have included below the specifications of the rifle straight from the Sig Sauer manual.

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Feature Image


Caliber: 5.56mm NATO

Overall Length: 37.0 ”

Length Stock Folded: 27.2 ”

Barrel Length: 16″

Rifling: 1 in 7″

Weight: 8 lbs



This article is courtesy of Rick Dembroski from The Arms Guide.