SIG introduced the 516 at the 2010 SHOT Show. The 516 is actually a line of rifles with varying configurations aimed at specific markets. They are gas-piston operated with a 3-position (4-position optional) gas regulator and employ a piston to reset the bolt as opposed to the DI method that vents much of the gas into to bolt chamber to reset it. While much ink and plenty of electrons have been spilled on the pros and cons of piston ARs version DI models, the basic advantage claimed by team piston is that venting the gas directly into the bolt also vents a lot of crap in there as well. That leads to a buildup of gunk in the bolt carrier area which could eventually lead to a failure to fire if the gun is not kept reasonably clean . . .
The major negative of the piston system is that there’s no real standard here. Where most manufacturers of DI weapons have fully interchangeable parts, each piston manufacturer employs their own design so you’re somewhat locked into a vendor. I’m not sure this is a really serious disadvantage for people who are content with purchasing complete uppers as that’s where the entire piston system lives.
You can certainly mix and match uppers and lowers, but if you are the sort of person who enjoys building and modifying your own uppers, then you may find some difficulty if you choose a piston system that doesn’t have a lot of third party parts support. The other disadvantage is that piston systems are more complex meaning that there is certainly more that can go wrong with them. Plus, they tend to cost a couple hundred dollars more than DI systems.
As in most things, of course, YMMV. If you are in an intense firefight and dumping hundreds of rounds downrange without much time to clean your gun, the piston may be a good choice. For most of us, provided we start our day with a clean rifle, we’re probably not going to shoot enough rounds in a single session for the buildup of gunk in a DI rifle to bother us
That said, the 516 definitely does not get as dirty as my Colt did and I don’t always have the chance to clean my rifle after every session, so having a gun that stays cleaner longer is a good thing. Just like 1911 vs. Glock or thin vs. thick crust, the question of DI versus piston won’t be settled any time soon.
But let me add two contradicting thoughts. First, the DI model has been in heavy use since the Vietnam era. If the DI model was seriously flawed, the DOD would likely have looked at replacing it with a piston version in the standard issue weapon system. On the other hand, Vietnam was wet jungle. It’s only been the last 20 years or so that our soldiers have had to fight in a totally different environment – one filled with sand. Lots of sand. It would seem that, with fine particulates in the wind, the less crap that gets blown into your bolt carrier group, the better.
Whether piston systems are superior to DI models in that sort of environment is still an open question. SIG did provide an impressive marketing video showing that the 516 can be buried in the mud and sand as well as submerged in water and still fire full auto with no problems. Is it a better system? That’s a question for people with a lot more expertise than I have. I will point out, though, that the newer 300 Blackout system developed by AAC in conjunction with the U.S. military uses a piston rather than a DI system.
SIG makes the 516 available in both semi-auto and select fire variants. The fire control/safety selector is an ambidextrous design. On the plus side, since the rifle is built with select fire in mind, you can use something like the Slide Fire bump stock to dump ammo downrange at near full auto rates if you want without fear that you’re going to fry your barrel.
All models come standard with a free-floating, aluminum quad rail fore-end with four M1913 Picatinny rails. Barrels are chrome-lined and cold-hammer forged with a Nitride finish for extreme durability and corrosion resistance and heavy match barrels are available with some models. The muzzle is threaded with a standard (0.5x28TPI) pattern to accommodate a wide variety of flash suppressors, muzzle brakes and suppressors.
The lower is machined from a 7075-T6 Aircraft grade aluminum just like the upper. The upper and lower feature a black, hard-coat anodized finish. Back-up iron sights are available for any model and come standard on the 516 Patrol model that I purchased.
SIG being SIG, they added a few nice features to the rifle. First, the lower has a couple of pressure buttons under the two take down pins. These are spring loaded and apply upwards pressure against the take down pins. The upshot is that there is absolutely no slack between the upper and lower. Sure, there are aftermarket parts available to add this functionality to any AR, but its nice that SIG included them in the design.
Another feature found on most of SIG’s AR-style rifles is multiple connection points for slings. You can use one, two, or three point slings and SIG’s method of attachment are push button release connectors. Again, a small thing but appreciated nonetheless as I needed to add an attachment point for a single point sling to my Colt.
SIG also designed the bolt carrier group themselves, choosing to make it an integral part of the bolt carrier group rather than simply riveting it on. While the rivet method works fine with DI systems, piston systems strike it much harder and SIG found that some of the earlier riveted designs failed due to the force of the piston.
The trigger is a fairly stout 7.6 lb single stage affair, but two-stage triggers are available in some models. The trigger is decent, but nothing to write home about. I would have preferred a better one in a gun with a list price just south of $1,700. It’s a shame, actually, as the rifle is capable of good accuracy, but you are not going to win too many national matches without changing it out.
The 516 weighs in at 7.3 pounds without a magazine, which is a bit heavier than my Colt. Accessories include one 30 round polymer PMAG and a single/double point sling. It ships in a nice hard-sided case that, while not of Pelican quality, certainly saves you some cash on an accessory purchase.
Compatibility with aftermarket accessories is pretty good. I purchased a CMMG .22 conversion bolt carrier group for my Colt and I’m happy to say that it works just fine with the 516, too. A relatively recent purchase (inspired by Foghorn’s incessant love affair with the 300 Blackout round) was an AAC 16″ 300 BLK upper. It snapped right onto my 516 lower and performed flawlessly.
Unfortunately, the same can’t be said for the Slide Fire bump stock I bought for my Colt. I tried to install it on the SIG and found the first problem – the built-in mount points for the single point sling interfered with the motion of the Slide Fire and it simply did not work. While I’m confident that a little time with a Dremel would have enabled me to modify my Slide Fire, I’m reluctant to do that to a $300+ accessory that I might one day want to sell if I get sick of dumping ammo downrange.
My solution was to pick up an inexpensive lower that takes the Slide Fire easily. Side benefit: now I have two complete ARs rather than one AR with two uppers. One other thing is that while the Slide Fire is capable of being locked into position to allow semi-automatic fire, it’s not as good as the multi-position stock that ships with the SIG, so it’s good to have the second lower.
The SIG has a 1:7 twist rate which means that it’s better at stabilizing heavier bullets. You can shoot just about anything through it, but the heavier rounds definitely afford more accuracy. In my testing, I found that the most accurate shots were obtained with Federal Premium Gold Medal .223 69 grain bullets. The 516 has no problem unloading cheap milsurp and Russian steel-jacketed rounds down range, but your accuracy will suffer.
Overall Length 37.5 in
Trigger Type MIL-SPEC
Trigger Weight 7.6 lbs
Barrel Length 16.0 in
Rifling 1 in 7 in
Number of Grooves 6
Weight without Mag 7.3 lbs