SIG SAUER P556
KAK Super Sig SB-15 Pistol Buffer Tube
The SIG SAUER P556 is a popular choice for people who want to register a short-barreled rifle. If you buy the pistol version and then begin the paper work, you can keep the P556 and shoot it, too, while you wait for the NFA stamp to come in. Now, thanks to SIG’s SB15 Pistol Stabilizing Arm Brace, the P556 has a much more promising life of its own. If you want a combat-capable compact rifle, this strange pistol has a lot to offer, right out of the box.
Let’s start with a basic look at the specs. The P556 traces its lineage to the SIG SG 550. In the States, SIG Sauer has made a number of variants. The pistol version is a 5.56 with a 10-inch barrel (1:7 twist). The flash suppressor is threaded on with .5×28 threads for those who want easy compatibility with silencers.
The block on the front end holds an adjustable gas system, the front sight (which is adjustable for windage) and a vestigial bayonet lug (as the barrel isn’t long enough to secure the hilt of the bayonet). Inside the gas tube is a long-stroke piston. If the gun gets filthy dirty, dirty enough to slow the piston, the gas system can be easily adjusted to improve reliability.
Fieldstripping is simple. The lower hinges open with the pop of a pin. If you want to drop the lower completely, you’ll need a screwdriver. Inside the lower, the trigger looks more like that of an AK than an AR, only with much tighter tolerances. If the Swiss were to have engineered the AK, it might have looked more like this. The trigger itself is a two-stage trigger that backs into a spring-loaded plunger. That plunger can be tightened or loosened to provide more or less resistance. I’ve not gotten into that modification yet. The trigger on this one breaks at 6.5 pounds, and it is a predictable break, so I’ve left it alone.
A simple catch holds in the charging handle. When that is removed, the rotating bolt slides out the back. Because the gun works more like an AK and less like an AR, there’s no need for a buffer tube. If you are looking at other SIG’s in the 556 line, many have folding stocks. These either have longer barrels (and longer over-all-lengths), or they have to be registered as short-barreled-rifles (SBRs) from the start. The P556 comes with a tube for use with the SIG SB15 Pistol Stabilizing Brace (more on that, below). If you don’t get a P556 with a tube, it will come with an aluminum cap on the end.
The lower is anodized aluminum. The safety is ambidextrous. I’m not used to how the lever falls on the right side of the receiver. Even now, after working with this gun off and on for more than a month, I hit the first knuckle of my right hand when I drop the safety with my thumb. If it were my gun, I’d simply remove the lever from the right side of the receiver and call it a day.
The barrel on the P556 is cold-hammer-forged stainless steel and button rifled. The overall length with the arm brace is 28 inches. Empty, the P556 weighs in at 6.8 pounds. It accepts all standard AR mags, which makes it very adaptable. The chunky Swiss-style forend fills the hand and comes with three sections of rail that can be attached on the sides or bottom for adding lights or lasers. To cap it all off, sling mounts are positioned front and rear.
Shooting the P556
I’ve shot some light AR pistols. This is not one of them. If you’re serious about shooting the P556 as a pistol, it is possible. With the 10-inch barrel and the forward placement of the magazine (as opposed to a bullpup design, or a magazine in the grip), the gun’s balance point has more in common with a rifle than a pistol. You can support the weight with a hand on the forend, but it still doesn’t stabilize as well as I’d like. Keeping both hands on the grip is ludicrous. As hard I try to shoot it like a pistol (and by this I mean without the brace), I simply can’t make it work like I’d like.
A bit of history on this review. We put in the request for the P556 a while ago, before the arm brace craze. When SIG sent us the review gun, it came in without a brace. As far as I can tell from the web page, SIG has begun listing the P556 with the arm brace. Without it, the gun is something of an anomaly. With the arm brace, this becomes a formidable weapon. I began the review with the gun in its stock configuration, but it didn’t take me long to get back on the phone with SIG and ask for an arm brace. They sent a brand new SB15 Pistol Stabilizing Brace out the same day.
Still, you will need some sort of buffer tube in order to make the whole contraption complete. We ended up with a P556 and a brace, but no tube. I thought about calling SIG again. Then I thought about duct tape. Lucky for us, KAK Industry had just released its second-generation Super Sig Buffer Tube. As far as pistol stabilizing brace tubes go, KAK has best option. This overbuilt tube is dimensionally specific for SIG’s brace and has a positive stop that keeps the brace from sliding too far forward. KAK also sells sleeves that slide down the tube to add more length of pull. I’ve tried the brace on AR pistol buffers and on the KAK tube. The KAK is easier to use, and the brace stays where you put it. Check out our review of the KAK tube here.
The only note that I would add here is that SIG puts the end caps on with some kind of magical Loctite. The cap is smooth, and has domed edges. A spanner wrench, and arms like a gorilla would both be helpful here. I couldn’t break the seal with a spanner, so gripped the cap in a monster pair of vice-grips. I eventually got the cap off (though it isn’t going to go back on). Skip this hassle if you can. If you’re in the market for a P556, get one with a tube already installed. Much easier.
The P556 as improvised SBR
Here’s the best part. The P556 is what it is. As an actual pistol, I’d say it is too much to handle reliably or effectively. With the addition of the brace, the gun becomes much more stable. The arm brace is split open like a U and slides down your forearm. Velcro straps hold it in place. With the brace locked down, you can shoot the P556 one handed. It isn’t a stretch at all. You can hold it secure at your hip and blow through rounds, or you can hold your arm out straight and use the sights. It is almost impossible to hold like a typical rifle, as it is strapped to your forearm. You can pull it in at an angle, but getting your head down to the sights can be cumbersome. But you won’t need to. One handed shooting works well enough.
But it just keeps getting better. Apart from the occasional range visit, I doubt many P556 owners will spend much time with the brace strapped down to their forearms. Instead it simply balances out the gun, and gives you a viable way to shoulder the P556. The brace, when placed against the shoulder, feels a lot like a stock. And it works almost as well. I’ve seen shooters shoulder the naked tubes of AR pistol buffer tubes, which leaves the bare aluminum punching in with every shot. It isn’t comfortable. But the arm brace, when shouldered, feels (and shoots) like a stock.
All of this is to say that the SB15 Pistol Stabilizing Arm Brace makes a decent shoulder stock. Look at the use of specific key terms there in that title. It isn’t called the SB15 Improvised Short Barreled Rifle Improvised Shoulder Stock. It works, though, no matter what you call it. When you put the P556 with a brace to your shoulder, the true potential of the platform truly shines.
Is it legal to shoot the P556 as if it were an SBR?
Let’s get the legal ruling from the ATF.
When SIG launched the brace, it was clear what end users would do with it. Yes it stabilizes the gun by locking it to the forearm, but that takes time. Anyone in a hurry would just throw it up like any other rifle and shoot from the shoulder. Would that be legal? Would simply putting the brace on a P556, or any other AR style pistol, make it a short-barreled rifle? The ATF has ruled on the issue, and they say no.
SIG SAUER’s original ATF compliance letter can be read here.
Their ruling can be summed up succinctly enough. It says that the brace is designed to be used as an arm brace, and that an arm brace doesn’t make it an SBR. Still, questions remained about the use of the arm brace as a stock. Would shouldering the weapon suddenly change how it is classified? SIG wrote back to the ATF. The response:
“FTB classifies weapons based on their physical design characteristics. While the usage/functionality of the weapon does influence the intended design, it is not the sole criteria for determining the classification of a weapon. Generally speaking, we do not classify weapons based on how an individual uses a weapon.”
“Generally speaking,” the ATF doesn’t classify weapons based on how an individual uses the weapon. That is a powerful statement, and it makes shouldering the P556 with an arm brace completely legal.
And it makes all the difference. The P556 comes alive. Shot placement becomes as reliable as it is with an AR. When your shooting hand isn’t locked in position by the brace, you can reach the controls more easily. And you can drop the gun if you need to. The one big flaw in the arm brace is that it is cumbersome to get on and off.
The Actual Results
After you’ve taken in the whole pistol stabilizing brace phenomena, the P556 can be evaluated on its own merits. The pistol, which operates most efficiently when it is being used like an SBR, is formidable. It is heavier than some AR-patterned SBRs. The overall length of the pistol with the brace comes in well below the typical AR carbine, but noticeably longer than a 7 inch barrel on an AR. The handguard on the Classic version is bulky. All of this is to say that it is smaller, but not small (and certainly not smallest).
I find that the P556 works best on a single-point sling attached at the base of the KAK tube. In this position, the P556’s grip is easily accessible, and the gun is easily moved aside for a pistol transition. It shoulders easily enough, even for a big guy like me.
The front sight is built into the gas block. It is perfect for a gun like this. The front blade is big, and ringed by a wide band. You could use it well enough with out a rear sight, but the P556 has one built into the rail on top of the receiver. The rear sight is just a thin post with an adjustable aperture on the end. Considering how overbuilt the front sight is, this rear sight feels a bit anemic. Yet the combination provides 18.1 inches of sight radius and is good for getting rounds on a torso-sized target at 100 yards.
The sights on the P556 are functional, but I’d rather use them as back-ups than as a primary sighting system. While the P556 doesn’t lend itself to magnified optics, they’re not out of the question. As this is a gun best suited for QCB, the myriad of red dots and holograms would seem like a better place to start. SIG includes a red dot with the gun, and it is a solid place to start. The best I can say about the optic is that it works. It holds its zero. We’ve put a lot of rounds through the P556, and twice we thought we’d killed the batteries on the SIG optic. It would simply fade out. When we cut it back on later, it would work fine. After the second time, we pulled it and topped the pistol with an Aimpoint PRO. That worked much better. It gave us a bit more height and a much brighter dot.
In all, I’d say we’ve put close to 700 rounds through the P556 so far. We shot it as a pistol, with the arm brace, and now as an improvised rifle, and we’ve yet to have a single problem. The gun ejects violently (even denting spent cases with the charging handle). It feeds well. Though the controls are more reminiscent of the AR-15 (with the magazine drop and safety lever), the trigger and charging handle feel more like they evolved from an AK platform. The combination can take a while to get used to, especially when running drills. The bolt drop lever rocks up and in, toward the top of the receiver, for example, and it is a different motion than an AR’s bolt release.
Accuracy with the pistol was abominable. This, of course, is not the gun’s fault. If you happen to be built like Andre the Giant (only with incongruously thin fingers), you could do good work freehand. With the brace on, groups tighten up. I was able to get five shots in less than 3 MOA with the brace. With the brace shouldered (still working with the native iron sights), I can get five shots with a two-inch radius. With the red dot, I can confidently place shots within a five-inch circle from 25 yards, and do so quickly.
That’s the real appeal of the P556. Speed. This isn’t a gun meant for target shooting or even plinking. It is meant for CQB, fast offense and effective defense. The compact size and heavy-hitting round make this gun better than pistol caliber carbines and ideal for LEOs or others getting in and out of vehicles, who might also need the potential to engage targets out to 100 yards (or right up in their faces). It is a halfway point between a pistol and a full-sized rifle and can cover much of the responsibilities of both.
How much will it set you back? The P556 alone has an MSRP of $1,207. With the brace, it is $1,340. In short, the P556 is a curious beast. It is a badass. SIG has clearly taken the best attributes of several systems and combined them into something that runs incredibly well.