Firearms Review: The piston-driven SIG716

SIG started making piston driven AR-15s in 2009 with the SIG516 and released the SIG716 at the SHOT Show in 2012

I recently had the chance to shoot and review piston driven ARs from six different manufacturers, one of which was from SIG Sauer. While those firearms — including the SIG — were chambered in 223/5.56, SIG has now provided me with a test sample of their new 308. This rifle is dubbed the SIG716 and is a piston driven semi-auto rifle built in the familiar AR pattern.

I find it interesting that things have now pretty much come full circle with the .308/7.62 cartridge and the AR platform. The AR got its start sixty years ago when Eugene Stoner used his aircraft engineering background to produce a rifle made of light space-age materials. This new rifle was called the AR-10.

Made mostly of aluminum, the design was revolutionary in its use of a gas system that harnessed the pressure of the gas itself to cycle the action rather than requiring the gas to push on a separate piston rod. The AR-10 was chambered in the 7.62 NATO cartridge with the hope that it would become the rifle to replace the M-1 Garand.

In addition to the included Magpul magazines, the 716 comes with the Magpul MIAD pistol grip and ACS buttstock.
In addition to the included Magpul magazines, the 716 comes with the Magpul MIAD pistol grip and ACS buttstock. (PoliceOne Image)

A Revolutionary Design
Unfortunately for Mister Stoner, his rifle was unable to unseat the M-14 and the AR-10 became nothing more than an interesting footnote in the history of US military rifle development. Despite the AR-10’s lack of acceptance, Eugene Stoner’s design showed great merit and was soon rebuilt and scaled down to become the M-16. The M-16 has been in US service longer than any other rifle and continues to soldier on as the M-4 Carbine.

While the M-4 is generally liked, there are those who decry the M-4’s 223/5.56 cartridge as lacking in both range and penetration. These shooters want something with substantially more punch and had previously been forced to choose between the M-14, FN FAL or Heckler and Koch G3 if they wanted a semi-auto rifle in a bigger caliber.

This brings us back to the AR-10’s beginnings with a number of companies like Knight’s Armament, Armalite, and DPMS, among others, now producing a modernized version of the old AR-10. As the M-16 or AR-15, in civilian hands, is generally a scaled-down AR-10, the modern AR-10 is generally a scaled-up version of the M-16 with most manufacturers designing their rifles to use as many AR-15 parts as possible.

These new AR-10s answer the call for those seeking a rifle with familiar handling that’s offered in a tried and true battle rifle cartridge. Perfect!

Nothing remains perfect forever, and there is now a growing market for piston-driven AR rifles. Regardless of caliber, one of the continuing complaints against Stoner’s direct gas system has been that of fouling and required maintenance. Since Stoner’s original design blows hot gases back into the rifle’s bolt and upper receiver, weapons using this system can become heavily fouled and unreliable if not cleaned on a fairly regular basis. Another problem that can arise with the direct gas system is the issue of too much gas pressure when using a sound suppressor.

Higher than optimal gas pressure can lead to dramatically increased cycling rates and reliability problems. Many manufacturers are dealing with these complaints by replacing the Stoner direct gas operation with a piston rod that cycles the bolt. Most of these new designs have been offered in 223/5.56 and it was only a matter of time before rifle makers started applying the piston drive to the big AR-10 design. Enter SIG and the new SIG716.

SIG started making piston driven AR-15s in 2009 with the SIG516 and released the SIG716 at the SHOT Show in 2012. As the names imply, the 516 is offered in 223/5.56 and the 716 is offered in 308/7.62. While the guns are similar in design and obviously related, the 716 is more than just a scaled-up 516. Methods of operation between the two rifles are the same but the 716 uses an improved gas valve.

One of my complaints about the 516 is that the gas valve on that rifle is threaded into the gas block. I’ve found that the threads get dirty with extended use and the valve can become difficult to unscrew. Not so with the 716. The 716’s valve uses studs that mate with grooves in the gas block. Simply rotate the gas valve 180-degrees and remove the valve. Like the 516’s gas valve, the 716’s valve offers four gas settings. These settings allow the shooter to adjust the gas pressure as the situation dictates and the shooter can choose from settings for normal and suppressed use.

The SIG716 accepts twenty round Stoner pattern AR-10 magazines. Any Stoner pattern magazine (not the Armalite AR-10 magazine based in the M-14 magazine) should fit and function. The 716 ships with magazines from Magpul and these magazines worked flawlessly in my testing. I didn’t have any other brands on hand to test but fully believe that Stoner magazines from other makers will work just fine. In addition to the included Magpul magazines, the 716 comes with the Magpul MIAD pistol grip and ACS buttstock.

The SIG716 also comes with folding back-up iron sights made of steel and aluminum. The SIG716 has a modern blocky appearance, a free-floated railed handguard, ambidextrous magazine release buttons and sling swivel sockets built directly into the lower receiver. The SIG716 features a chrome lined sixteen inch barrel that is threaded 5/8-24 to accept most 308 flash hiders and muzzle brakes.

I fired the SIG716 for accuracy at 100 yards using the Leupold 1.25-4x20mm VX-R scope. Accuracy was good but not outstanding with groups using 168gr and 175gr ammo running about 1.5” in most cases. During testing, I fired the 716 using a mix of Winchester and Remington factory ammo as well as WOLF steel cased ammunition imported from Russia. Steel cased ammo can sometimes cause extraction failures but I had zero issues with the SIG in the 400+ rounds I fired.

In addition to testing for accuracy off the bench, I also function tested the SIG716 with a 762-SDN-6 sound suppressor from Advanced Armament Corporation. The rifle worked flawlessly in all cases and gave me no problems whatsoever.

I enjoyed shooting the SIG716 but would like to comment on the rifle’s weight. SIG lists the rifle’s weight as 9.3 pounds empty. This places the big rifle’s weight at a full two pounds heavier than the SIG516.

This is, I’m afraid, the nature of the beast when dealing with semi-auto rifles in the 308/7.62 caliber. The rifle is heavy but it is a heavy hitter and should prove useful to officers patrolling in open or rural areas. In addition, hunters and sportsmen who find themselves in need of a semi-auto rifle that offers more range than that which is generally available in a 223/5.56 weapon will find this rifle to their liking.

As SIG’s product literature says, “Familiar handling, unfamiliar power.”

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