September 24, 2023

When I was younger and had more hair but fewer brains underneath it, I didn’t know AR-15s could be as reliable as the SIG 516. In fact, my first AR was a match-grade 20-inch DCM Bushmaster A2 clone, and while stupidly accurate, would require herculean strength to clear stuck steel cases from. This meant that the poor college student version of me was spending 40 cents per round on premium ammo, versus the 12 cents per round Tula steel case at the time. (God I wish that was still the going rate for both!)

But then one faithful day, I managed to win a complete SIG 516 Carbine at a shooting match, and it opened my wallet up to a whole slew of garbage ammo that I could merrily blast through my SIG and not clean the thing for months.

How? Read on to find out.

Sig516 Jim Grant
My SIG516 carbine has been ridden hard and put up wet. But it just keeps on chugging! IMG Jim Grant

Sig Sauer Sig516 Gen 2 Upper Receiver Assembly

Sig Sauer Sig516 Gen 2 Upper Receiver Assembly
Sig Sauer Sig516 Gen 2 Upper Receiver Assembly

Whereas your standard run-of-the-mill AR-15 is a direct impingement-operated firearm, the SIG 516 instead utilizes a short-stroke piston. If you’re familiar with PWS’s piston guns, the Taiwanese T-91 assault rifle, or the Russian SKS, the same principle applies here.

Visualize the AK-47, it has a long piston attached to the bolt carrier group. The piston lies in the gas tube, and when hot expanding gasses siphoned from the detonated cartridge enter said tube, the piston drives the bolt carrier group rearward. This in turn extracts the spent casing, and then the recoil spring propels it forward to chamber a new round from the magazine.

The SIG 516 works in a very similar way, except the piston is separate from the carrier group and contained within the gas tube with its own small return spring.

Your next question should be, why?

The main advantage of using a short-stroke piston over a long-stroke one is that the mass of the reciprocating carrier group is substantially decreased. This has the effect of reducing felt recoil since there isn’t a massive weight traveling back and forth between shots.

SIG 516 Upper VS Standard AR-15 Upper

SIG-516 Jim Grant
The 516 makes an excellent suppressor host – it ran flawlessly with my SilencerCo Saker ASR provided by SilencerShop. IMG Jim Grant

OK, but then the next question needs to be, why choose this over a standard direct-impingement setup. Primarily for reliability reasons, stemming from less sensitivity to carbon buildup and to an extent, less consistently-loaded ammunition. Though that last part is a somewhat moot point; Not because the statement is untrue, but because modern AR-makers have configured their guns to tolerate this ammunition in a number of ways. The most common way – especially among cheaper uppers – is to simply over gas the hell out of them.

To these makers’ credit, over-gassing does work. But it has some drawbacks like increased wear on components, and increased recoil impulse.

But one of the aspects of the 516 that makes it so great and reliable, is its integrated adjustable gas system. For shooters like myself who love to suppress everything they own, this is a must-have feature.

Why? Because it lets you reduce that rearward pressure to make the gun cycle normally despite the increased backpressure caused by adding a sound suppressor.

The SIG516 ships with a somewhat outdated quad rail. And although heavy, it’s also extremely durable. IMG Jim Grant

516 Features

The uppers come fairly barebones. They lack any sort of iron sights but do include a full-length Picatinny rail on top, as well as an old-school quad-rail. These uppers are (or were) available in various barrel lengths including 16, 14.5, and 12.5-inch. For the review, I chose the 14.5-inch barrel version and had a SilencerCo ASR Flash Hider pinned and welded to the barrel to bring it to the NFA-required 16-inch barrel length. Normally, I would just toss a brace on the gun and call it a day, but since I was going to run this gun suppressed primarily anyway, I figured I’d just make the muzzle device permanent.

One thing some shooters will notice is that the quad rail isn’t for standard AR-15s. This is because it needs to accommodate the adjustable gas valve at the front. And if you’re like me and think that a quad rail is a little too heavy, Lancer Industries offers carbon fiber handguards specifically for this gun – though they (predictably) aren’t cheap.

Lastly, all barrel configurations ship with an A2-style birdcage combination flash-suppressor/compensator. It doesn’t work especially well, but more than well enough to curb the recoil on the mild 5.56mm round.

Everything on the 516 is AR-15-compatible except the BCG and the handguard. Thankfully, Lancer Industries makes a very nice carbon fiber handguard for the gun. IMG Jim Grant

Sig516 Performance

I own two 516s, one is just an upper, while the other is a complete gun from SIG. I have fed my personal gun over 8,000 rounds without a single malfunction over several years, and in a DMR match where my primary weapon went down, I was able to successfully engage targets out to 600 yards using the standard 16-inch barrel SIG 516 carbine equipped with an Elcan Spectre Four-Power Scope.

As for the 14.5-inch upper, it has only thus far fired around 750 rounds over the course of six months, but in that time also has encountered no problems whatsoever. It doesn’t seem to care if I feed it high-end match-grade ammo, brass mil-spec rounds, or crappy Monarch re-branded steel-cased Tula .223. It just keeps running and running. As far as accuracy, the 516 upper had no problems engaging man-sized targets at 450 yards with a reflex sight, provided that a shooter did their part.

The SIG516’s gas regulator is simple to use and doesn’t require any special tools. IMG Jim Grant

SIG516 Verdict – Pure Upgrade?

As much as I love the 516, objectively it’s not a pure upgrade over a standard DI upper. Yes, it runs cleaner, more reliably (especially with a can), and is extremely robust, but it’s also substantially heavier. The SIG 516 upper without optics or accessories tips the scales at four pounds, 15 ounces. Compare that to a modern extruded-aluminum handguard 14.5in upper which weighs right around three pounds. The extra two pounds might not seem like much, but since that weight is primarily towards the muzzle, it can feel very heavy very fast. Not to mention the fact that a DI upper will tend to be a little more accurate, but provided that a quality barrel is used on both guns, neither will produce groups larger than two MOA with quality ammo.

My opinion on the Sig Sauer Sig516 Gen 2 Upper Receiver? For shooters looking for a great suppressor host, it is rock solid – it’s just too bad that the barrel profile is proprietary since the gun would be amazing in .300blk.

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About Jim Grant

Jim is one of the elite editors for, who in addition to his mastery of prose, can wield a camera with expert finesse. He loves anything and everything guns but holds firearms from the Cold War in a special place in his heart.

When he’s not reviewing guns or shooting for fun and competition, Jim can be found hiking and hunting with his wife Kimberly, and their dog Peanut in the South Carolina low country.

Jim Grant

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