By Doug Larson , Personal Defense World
There’s just something about AR-style pistols that interests a number of AR-15 enthusiasts, and that interest creates enough demand to spur some AR-15 manufacturers to produce them. The enthusiasm for the pistols could have something to do with the fact that although they are not easily carried, aimed or readily concealed, they can have a self-defense role in certain special situations. Whatever the reason, the demand has caused Sig Sauer to offer a pistol version of its highly successful and rugged AR-15 rifle. In 2010, Sig Sauer introduced the SIG516 piston-driven AR-15. It was the company’s first AR-style gun and was thoroughly tested for dependability. I witnessed an endurance demonstration where the gun was buried in sand, submerged in water and buried at the bottom of a pond in mud before being fired, all without a single malfunction; no cleaning or lubrication was required to keep it running. The pistol is of the same basic design and pedigree, so it should be a tough gun.
“Surrounding the SIG P516’s free-floating barrel and piston is a 7.25-inch-long handguard with Picatinny rails on all sides.”
Although a 7-inch barrel is offered, the pistol received for testing had a 10-inch barrel. That length is the same as one of Sig’s short-barreled rifles, but the pistol does not require ATF approval for civilian ownership. The barrel is chrome-lined and makes one twist in 7 inches, which is good for stabilizing longer, heavier bullets. It is finished with manganese phosphate for durability and corrosion resistance. Attached at the front is an A2-style birdcage flash suppressor that makes a pretty good attempt at reducing the flash signature, which is difficult with such a short barrel. A removable flip-up front sight is attached to the short Picatinny rail on top of the gas block. Inside the gas block is the gas valve (or plug) that connects to the piston, which sends the bolt carrier group to the rear, cycling the action. The plug can be rotated to one of four positions and features a round hole into which a cartridge can be inserted to help turn it.
When the valve is in the vertical position, the system is set for normal operation. Turning it one notch clockwise (when viewed from the rear) aligns a slightly larger hole in the gas valve with the gas port in the barrel to deliver a bit more power to cycle the gun. This is helpful if the gun is dirty and isn’t cycling optimally, since the shooter can’t really stop to clean it. Sig recommends not running the gun with the valve in this position for long because it puts extra wear and stress on parts. Turning the plug from the normal position counter-clockwise one notch aligns a smaller hole in the valve with the gas port, reducing the amount of power delivered to the piston and bolt carrier group. This position is used when a sound suppressor is attached. With a suppressor, there is more rearward pressure, and not as much gas is needed to run the gun. To move the plug to this position, a small plunger on the front of the gas block must be depressed.
If the gas plug is turned two clicks clockwise from the normal position (this also requires that the plunger be depressed), gas is prevented from entering the gas system, which keeps the bolt carrier group from cycling and brass from flying when a round is fired. This position is used to obtain the highest degree of sound suppression when using a suppressor. Some believe that this cut-off position also enhances accuracy, but the gun must be cycled by hand. The piston itself has three gas rings and fits snugly into the gas valve. One of the advantages of a gas piston system is that fouling and hot gas are not routed into the receiver, as is the case with a direct-gas-impingement gun. This reduces stress and heat on the bolt carrier group, allowing the gun to run without as much lubrication, and makes cleanup easier. The hot gas instead impacts the piston, so carbon builds up there instead of in the bolt carrier group. Wherever the carbon accumulates, though, it still needs to be removed periodically in order for the gun to keep running. Piston cleaning cannot be neglected. Surrounding the free-floating barrel and piston is a 7.25-inch-long handguard with Picatinny rails on all sides. Sig supplies ERGO ladder-type protective covers for the T-marked slots, of which there are plenty for mounting accessories. But do not put a vertical foregrip on this pistol—that’s a ticket to jail! The two side rails have quick-detach sling swivel sockets at the front and back for the attachment of a sling, and there are also sockets on each side of the lower receiver, just in front of the buffer tube. A sling is a very good idea on this pistol because a holster is pretty much out of the question and some convenient method of carrying it is needed. The upper receiver has a standard AR-15 appearance with a T-marked Picatinny rail running the length of it. At the rear, Sig supplies a removable flip-up iron sight with large and small apertures. The gun is also equipped with the standard charging handle, bolt forward assist and brass deflector; however, inside the upper receiver the bolt carrier group is decidedly not standard when compared to a direct-gas gun.
The carrier does not have a gas key. Instead, it has a boss that is machined directly into the carrier where the gas key would otherwise be. The carrier is faceted, not round, and has lightening cuts. It is treated with what appears to be a black nitride finish instead of phosphate, and it is not chrome-lined because it doesn’t have to be. Also referred to as Melonite, the black nitride finish is extremely hard, durable and corrosion resistant. The rear of the carrier is also slightly larger than a direct-gas bolt carrier in order to fit inside the buffer tube more snuggly. This reduces carrier tilt, which is an unfortunate consequence of the change from a direct-gas to a gas-piston system. However, the modified carrier solves the tilt problem even if it does require that the rear of it (and the interior of the tube) be lubricated. The bolt looks like a direct-gas bolt, and the extractor is equipped with a black spring insert and a rubber ring to increase gripping power on the rim of spent cartridges.
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