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First Look: SIG Sauer's New $800 M400 TREAD

A base-model AR-15 worthy of the SIG Sauer name.

First Look: SIG Sauer's New $800 M400 TREAD

SIG Sauer knows how to do a lot of things well and producing high-quality AR-15s is just one of them. The company’s M400 AR has been wildly popular both domestically and internationally, with a surprising number of sales going to foreign military and law enforcement agencies the world over. To say the platform is field-proven would be an understatement.


It is no secret, domestic AR sales for many manufacturers have diminished a bit. That’s not necessarily a bad thing given the number of people who own an AR-15 today. What it means is there are more AR-15s in the hands of responsible individuals than ever before and that’s a good thing.

To keep these same people interested while catching the attention of new shooters, manufacturers have had to sharpen their pencils and provide consumers with more bang for their buck. SIG Sauer’s new M400 TREAD does exactly that.

As mentioned, TREAD is a product focused on the entry-level buyer, but aside from its price point, it is far from entry level. One glance at the rifle and you won’t find crummy, short-plastic handguards, a chintzy M4-style stock, or a budget A2 pistol grip.

Instead, you’ll find a carbine you’d expect to cost hundreds of dollars more but doesn’t. The M400 TREAD is feature-rich, making it far from basic, but it’s entry level for SIG. Let’s take a look at what makes the TREAD so special.

Rifle’s Heart

The heart of every rifle is its barrel and the TREAD has a healthy one. In fact, SIG Sauer uses virtually the same barrel used for its premium VTAC model, missing only the enhanced surface treatment. Other than that, shooters get an incredibly accurate, 1:8-inch twist, mid-length gas barrel with a low-profile gas block that has been pinned in place.


Why a Mid-Length?

Stretching the length of the gas tube from 7 inches to about 9.8 inches means the bullet moves further down the barrel before the action cycles. When the bullet moves down the bore, the pressure inside the barrel drops. A longer gas tube means lower operating pressures, which translates into less wear on both the parts and the shooter, the later benefits from less felt recoil and muzzle rise.

ARs work best when pressures are kept low. Residual pressure in the chamber after a shot is fired is hard on the bolt lugs as they are twisted to unlock while still inside the barrel extension and is the prime reason why bolt lugs shear off.

Lowering the pressure in the bore extends the life of the bolt by making it easier for it to unlock and extract the fired case. With the data we now have, there is no reason to have a shorter carbine-length gas system in a 16-inch barreled carbine. Mid-length is the right choice.

Special Touches

The barrel of the M400 TREAD is tipped with SIG’s three-prong flash hider that is a proven design and one efficient at reducing the flash signature of the rifle firing. In the aftermarket, this upgrade alone would cost $100 or higher.


The rifle comes standard with an aluminum, 15-inch, M-Lok, free-floating handguard that attaches to a proprietary barrel nut with two hex screws. This handguard is extremely ridged, a desirable feature for mounting accessories such as iron sights or lasers.

The handguard is so rugged that it baffled several product managers a SIG, as it out performed proprietary and aftermarket models engineers had been testing. Should the shooter desire to swap out the TREAD handguard for something else, they can easily remove it without any special tools or armorers training.


Moving back to the receiver set, you get the same awesome ambidextrous lower receiver as other, more expensive M400’s, complete with dual sling swivel cups at the rear and my preferred selector switches. Perhaps, I’ve been spending too much time with my MCX, but I have come to prefer them.


The bolt carrier group is constructed of industry-standard Carpenter 158 tool steel and the gas key is properly staked. SIG’s own ergonomic pistol grip was added, as well as a Magpul enhanced triggerguard for use with gloved fingers.

The trigger is called SIG’s polished-hardcoat trigger. It is essentially a very good single-stage mil-spec trigger. It’s no Geissele, but it is more than acceptable in this off-the-shelf rifle at this price point.


Stocks, like grips are very user dependent. The M400 receives Magpul’s excellent MOE SL buttstock, which is a favorite of mine and an exceptional value.

It has a slender profile that puts plenty of meat against the firing shoulder and the adjustment lever is tucked up beneath the comb where unintentional activation is unlikely. A pair of metal sling swivel cups are located on either side of the stock for use with a quick-detach sling and two slots where a sling can loop around the stock for direct attachment.

I’ve been told the SL is Magpul’s second strongest stock, next in line to its UBR model. The latch system is so strong on the SL that it can be repeatedly bashed into the ground without the stock breaking. The positioning detent in the buffer tube will deform before the stock will actually break.

Aside from the stock’s ruggedness and lightweight, its slender profile lends itself well to high-mounted, red-dot sights or low-power variable optics in 1.93-inch height mounts. This allows head placement to be more centered and in-line with the optic.

But Wait, There is More


The M400 TREAD rifle purchased off the shelf is an incredible value and will serve any user well. But, the rifle in this stock configuration is only half of the TREAD story. The real allure is what the rifle can be.

SIG Sauer has produced a line of TREAD-branded accessories to allow the rifle to grow with its user. Each piece has been thoroughly tested and evaluated to work seamlessly with this platform and the simplicity of installation could not get any easier.

You’ll find these accessories at the retail point and they’ll be hard to miss. If you see the TREAD logo, you know the factory accessory is vetted to work with the gun.


Available TREAD-Branded Accessories:


M-Lok Handguard - $150

Available in 13- and 15-inch lengths, both feature extensive lightning cuts to help reduce weight and allow additional cooling. Installation is easy consisting of loosening a pair of hex screws at the front of the receiver and presto.


Ambidextrous Charging Handle - $50

Constructed of aircraft-grade aluminum and featuring a dual roll-pin design for longevity.

Handguard Accessories


M-Lok Hand stop kit ($30) that is completely customizable for the end user.


M-Lok Vertical Grip Kit ($30) includes a stubby vertical forward grip and hand stop for an aggressive high, thumb-forward or over-the-rail raked grip.


M-Lok Grip Kit ($50) consists of both the hand stop and vertical grip kits and provides all the parts necessary to build the optimal grip for you.


Carrying a suggested retail price of $150, the Romeo5 Tread is an incredible value. This miniature red-dot sight comes complete with an absolute co-witness height mount.


The proven Romeo5 features a 2-MOA aiming dot with 10 illumination settings. The sight also motion activated and has 50,000 hours of battery life on a single CR2032 lithium battery.

Flip-Up Backup Iron Sights

Even in this day and age of ruggedized electronic sights, it’s always a good idea to have a set of back-up iron sights ($150) on your rifle. I personally don’t think they are necessary, but piece of mind is worth the cost of admission to some folks.


SIG Sauer’s are of high quality and are the same units available on their top-tier MCX platform. These sights are low in profile, easy to install and simple to zero without tools.


M-Lok Front-Sight Adapter

I know it sounds strange that you’d need to purchase a separate front sight adapter, but you do. Due to the low-profile, ergonomic rail that ships with the M400 Tread, a custom M-Lok, front-sight adapter is necessary to attain the proper height necessary to zero your iron sights. A traditional piece of M-Lok rail will not do the job and the front sight will be too low.


Compensator ($50)

The M400 TREAD ships with an extremely effective three-pronged flash hider that would set you back $100 or more if purchased through an aftermarket manufacturer.

While a 5.56 has relatively low recoil, SIG’s new three-chamber compensator does an excellent job of mitigating muzzle rise and felt recoil. In fact, the compensator – coupled with the TREAD’s mid-length gas system – all but does away with recoil altogether, and the combo will surprise you and your shooting buddies just how fast you can get rounds on target.


Single-Stage Trigger ($120)

One of my first upgrades for the M400 TREAD would be this single-stage trigger. Not because the unit that ships with the base model is bad, because it is not. I really like the shape of the trigger shoe and how my finger positions on the flat blade. It is comfortable, repeatable and allows the rifle to be shot quickly and precisely.

Off-the-Shelf Base Rifle


Accessorized Tread
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