June 10, 2019
By James Tarr
Unless you’ve been completely ignoring the firearms market for the past five years or so, you will have noticed how SIG Sauer has been doing everything it can to take over every market segment even slightly related to guns. The company is advertising itself as “The complete systems provider,” and considering it’s selling everything from ammunition to optics to suppressors in addition to firearms, it’s more than just hyperbole.
SIG has been selling several AR-pattern rifles. The flagship is perhaps the MCX Virtus, which is a piston-driven gun that has all sorts of bells and whistles. It is also expensive and rather heavy.
SIG also has the M400 direct-gas-impingement AR. These rifles have offered a few upgrades over standard mil-spec but have been priced somewhat higher than similar competing designs from other manufacturers—particularly economy M4-style rifles.
Enter the SIG M400 Tread, which is meant to fill that open niche in SIG’s catalog and offer far better than GI M4 looks and performance at a more competitive price. The suggested retail price is just $951, which means the Tread will be on dealer shelves probably marked near or below $850.
SIG is going all out with the advertising for the Tread, and if you’re wondering where the name comes from, look at the logo on the side of the aluminum handguard. It’s a snake in the shape of the American flag, deliberately reminiscent of the 1775 “Don’t Tread On Me” Gadsden flag from the American Revolution.
Many of the shirts and stickers SIG is selling have the Tread logo in yellow or on a yellow background—mimicking the yellow field of the Gadsden flag—and I’m surprised SIG doesn’t put the logo on the lower receiver instead of—or in addition to—the handguard. Hint, hint.
Yes, there’s a catchy logo designed to get you shouting, “’Merica!” and throwing your cash at SIG, but does the SIG Tread offer anything of substance for its competitive price? Definitely.
The first thing that caught my eye when picking up the rifle from my FFL was the stainless steel barrel. The barrel has been left “in the white” for a little flash and good looks, although most of it is hidden inside the handguard.
Also under the handguard is a low-profile stainless steel gas block made by SIG. The gas block is of an unusual and somewhat fancy design, and while at first glance it resembles some adjustable gas blocks on the market, it is not adjustable.
The barrel is 16 inches long, with a 1:8 twist, 5.56 NATO chamber and a mid-length gas system. Here’s a quick primer on why you want all of that.
A 5.56 NATO chamber is a little bigger than the .223 Rem. chamber, which in addition to safely allowing you to shoot the higher pressure 5.56 round has a little more room and is thought to provide a little extra reliability when the rifle gets dirty. The 1:8 twist rate seems to be the best to handle a wide range of bullet weights.
The mid-length gas system is considered to be optimum for reliability and reduced recoil in a 16-inch barrel. Pressures are lower than they are in the shorter carbine-length gas system, and as a result the bolt moves more slowly, increasing bolt life and reducing felt recoil.
The barrel is tipped with a three-prong flash hider of SIG’s own design, and in testing the rifle I found it to be effective. The barrel is free-floated inside the long handguard.
The barrel profile generally is what determines how heavy or light your AR is going to be. The barrel of the Tread has a medium-light profile, and as a result the overall unloaded weight of the Tread is six pounds, nine ounces, even with the long aluminum handguard.
SIG currently lists the weight of the Tread on its website as seven pounds, but even with an empty magazine in place it weighs only six pounds, 13 ounces, so I’m guessing somebody rounded up. With the stock fully extended, the rifle balances over the front receiver pin, so it is not muzzle heavy.
The 15-inch handguard is a new SIG design and is found only on the Tread. It has M-Lok attachment slots at three, six, nine and 12 o’clock on the forward two-thirds of the handguard. If you want to mount a front sight on the handguard, you’ll have to first attach a rail section to the top of it near the muzzle; SIG sells both rail sections and flip-up sights—as do tons of aftermarket companies.
The lower receiver is where you’ll see some serious changes from the GI specs. The Tread features ambidextrous controls. The ambi safety’s right-side lever is short enough that it didn’t poke my trigger finger, which is a problem I have with most ambi safety levers.
The Tread also has an ambi magazine release, with a pivoting lever on the left side, and also an extended bolt release to make locking the bolt back a little bit easier.
Just 10 percent of the population is left-handed, but everyone who shoots an AR has to use the charging handle, so I don’t know why SIG would equip the Tread with improved ambi controls and then stick a single-sided and outdated GI-style charging handle on the gun.
A flared magazine well would have been more useful to everyone, too. I mention this not only because I think a slightly flared magazine well is needed on the AR in general but also because the magazine well on the Tread was noticeably tight.
There are big QD sling swivel sockets on either side of the lower receiver at the rear. A rubber tensioning device at the back of the lower receiver underneath the rear receiver pin eliminates any play or rattle between the two receiver halves.
According to SIG, the Tread is equipped with a “single-stage polished/hard-coat trigger,” and I wish I could say it provided a better than GI trigger pull. It doesn’t. Trigger pull on my sample was seven pounds even and a tiny bit gritty. A seven-pound trigger pull is great if you’re using a heavy trigger pull as additional insurance against a negligent discharge, but it sucks if you know what you’re doing or if you actually want to shoot tight groups at distance.
The provided stock on the Tread is Magpul’s new SL-K, which has a reduced profile. It rides on a six-position buffer tube. I was pleased to see the castle nut, which holds the buffer tube firmly to the receiver, properly staked.
The pistol grip is one of SIG’s own design. It mimics the A2 grip angle while providing a little more material under the web of your hand to promote proper placement of your finger on the trigger. The trigger guard is an oversize polymer piece.
The rifle is supplied with one 30-round magazine, a Magpul Gen 2 PMag in the case of my sample.
Looks are a big selling point for just about any firearm, and my opinions on what looks good and what doesn’t certainly aren’t shared by everyone. Having said that, I think the alternate 15-inch handguard with lightening cuts that SIG sells as a Tread factory accessory is the one it should have put on this rifle. It is both more functional (with more M-Lok slots) and has a more traditional appearance than the Tread’s factory standard handguard.
The rifle you see in the accompanying photos—and which I’ve described in this article—is the standard factory Tread, but SIG seems to be pushing its “Tread-branded” accessories and upgrades just as hard as it is pushing the rifle. Most of the photos of Treads I see on SIG’s website show the rifle sporting some of those accessories—triggers, muzzle devices, flip-up sights, ambi charging handle, vertical grips/handstops and the aforementioned alternate aluminum handguards.
Although I don’t really care for the looks of the provided handguard, it works just fine, and even as a picky, spoiled gun writer, the only functional upgrades I think the base rifle needs is a better trigger and an oversize charging handle. It should also have iron sights if you intend to use the rifle for self-defense. Subscribing to the “whatever can go wrong, will go wrong” philosophy, I believe every rifle should have backup irons no matter how reliable your optic of choice is.
That said, the great thing about the Tread and every other AR-15 rifle is modularity. You can swap out every part on the rifle using simple hand tools. If you’re in doubt as to exactly how, there are plenty of how-to videos on the internet, and when in doubt about the source, go to a trusted videomaker like Brownells.
For accuracy testing, I slapped on a Trijicon AccuPower 1-8X scope in a QD mount from Midwest Industries, and the rifle did very well. Accuracy with just about every type of ammo I tried averaged between one and two m.o.a., and the biggest challenge was getting that kind of accuracy while wrestling with a seven-pound trigger.
However, this is not a rifle intended for benchrest shooting, and for serious fun at the range, I mounted an Aimpoint CompM5 red dot. It is small, light and robust and has a battery life measured in eons.
I grabbed a menagerie of magazines for reliability testing. In addition to the provided Gen 2 Magpul PMag, I used a Gen 1 PMag, a Lancer AWM and a Colt aluminum magazine with a Magpul follower.
Outside the accuracy test, for most of the range work I used bulk-packed 5.56 NATO FMJ from Frontier Ammunition, which is a collaborative business partnership between Hornady and the Lake City Army Ammunition Plant. Frontier features Hornady bullets loaded into cases by the Lake City plant for budget-priced ammo.
A light, soft-recoiling rifle like the AR-15 is always fun to shoot, and hammering paper offhand is a great way to spend an afternoon. The only issue I encountered was with a first-generation Magpul PMag, which is a little larger than the new ones. As I mentioned, the magazine well of the Tread was tight. The Gen 1 PMag fit in the gun, but it did not drop free when empty whether the bolt was closed or locked open.
I believe the direct reason for the existence of the Tread and several other new ARs is the Springfield Armory Saint, which made a splashy debut two years ago with videos depicting the rifle as a lifestyle product. But the Saint wasn’t just a marketing gimmick. It was a significant improvement over a standard M4-pattern AR, sporting better-than-GI furniture and a mid-length gas system instead of the traditional carbine-length. It was close to $300 less than any competing rifle from any other major manufacturer and had a huge impact on the market.
Ruger responded with its AR-556 MPR, and now SIG has followed with the Tread. And, like Springfield, SIG is selling a lifestyle as much as a rifle with the Tread. The famous marketing line is “Sell the sizzle, not the steak,” but the good news is that with the Tread you get a little of both.
SIG’s ARs historically have been overweight and overpriced. The Tread is neither. For the price, I don’t know of any other company offering a similar AR-15 with ambidextrous controls and all the other features found in the Tread for anything close to the Tread’s price.