Range Report: SIG M400 Rifle — Beyond Service Grade

Woman resting against an old Ford pickup truck while holding a SIG M400 Tread .223/5.56 rifle

A technological and marketing term called feature creep has troubled me for some time when it comes to service grade firearms. The term refers to firearms being loaded with add-on features that are not really needed for the job. Adjustable sights and target-type triggers on the 1911 handgun, and extended controls and light triggers on service grade AR rifles are among these features.

Feature creep makes the firearm incrementally more complex until the original intent is obscured. A real impediment is a designer that thinks his firearm must do everything and anything. I am not an operator, and I have not been on the front line in institutional service in some time. But I know what is needed in personal defense, service use, and in a good general-purpose rifle that will serve many roles well. Treading through a high density of egos, I find that a general consensus of what is needed in a service grade rifle would give us a rifle similar to the SIG M400.

Woman shouldering a SIG M400 with an attached foregrip
As a go anywhere, do anything an AR can do rifle, the SIG M400 has great promise.

Several companies, originally founded to manufacture handguns, eventually offered AR-15 rifles. Colt, FN, Ruger, and Springfield are among them. You don’t need the most expensive rifle, but you need a very good one.


SIG’s M400 TREAD is among the most attractive rifles based on function and price point. The TREAD sells for less than $1,000 and offers reliability and performance. The name TREAD, by the way, is a play on the original American slogan Don’t Tread On Me. Since the TREAD is manufactured in the Granite State, home of Daniel Webster, this is a fitting name.

The rifle begins with the kind of barrel I would choose if building an AR-15. The stainless steel barrel is 16 inches with a 5.56mm NATO chamber, 1:8-inch twist, mid-length gas system, and a sturdily pinned gas block. This is the system I would choose for reliability.

The 5.56mm chamber is slightly less tight than a .223 Remington. If you handload, and use high-pressure loads, there is an advantage. The barrel choice dictates the weight of your rifle. The 16-inch light contour barrel is ideal for most uses. The barrel features a three-prong flash higher. It looks cool and seems to do the business.

The rifle comes standard with a 15-inch aluminum handguard that houses the free-floating barrel. That is a good gripping surface and offers plenty of real estate for mounting combat lights or lasers. The weight of the rifle, unloaded, is six pounds and eleven ounces.

multiple shooters shooting and moving between firing stations at a three gun range
Whatever the role you push the AR into, get training!

There are two things that ensure AR-15 reliability. One of these is a gas block pinned in place rather than screwed in place. The other is a bolt with the gas keys staked in place properly. I still see mistakes, and all are not home-built rifles. Some of the factory units are ‘economy rifles.’ 

The TREAD is properly set up for reliability. The handguard is long enough for good purchase and mounting lights, with M-Lok slots spaced on the forward section of the handguard. The stock is the usual six-position adjustable stock — this one by Magpul. The upper and lower receiver fit well together with minimal play.

The rifle features an ambidextrous safety. The magazine release is also ambidextrous. A good touch is a tension device just below the receiver pin that may be used to tighten the fit between upper and lower receivers.

Man performing a speed load of the M400 .223/5.56 rifle while running between positions
The AR is a very ergonomic performer. The SIG M400 couples faultless reliability with the AR rifle.

The trigger is — according to SIG — a single stage, and it is nicely polished. The trigger action breaks cleanly at six pounds and fourteen ounces of compression. The handgrip felt good as I tested the trigger, with plenty of gripping surface and a good fit for most hand sizes. The rifle is provided with one magazine. Like most of you, I have a box of PMAG magazines, and these were used for the test program.

SIG Optics

When I picked the rifle up from my FFL, I decided to mount a SIG Romeo red dot sight. My friend John decided I didn’t have to spend a ton to have a good red dot on the TREAD. By the same token, we agreed that I should not go too cheap.

This rifle didn’t come and go as a test piece. I kept the rifle and it is on the front line. I have used a good dozen or so of SIG’s Romeo red dot sights and always with good results. So, a good sight was appropriate for a rifle that was going to be a keeper.

SIG Sauer Romeo 5XDR red dot in the picatinny rail of the SIG M400 Tread rifle in .223/5.56
SIG’s Romeo optics are among the best balances of affordability and reliability.

The exact version I chose is the SIG Romeo 5XDR. This a 1x20mm red dot. The dot has eight standard illumination settings. For bright light, a larger more visible dot is my choice. The red dot may be quickly adjusted down for dim light. Battery life is 50,000 hours — a huge advantage for those of us using several different rifles and dots, and perhaps not keeping as close a watch on battery life as we should.

A good rule of thumb, change the battery on your birthday. The dot is 1 MOA, and we have a total travel of 100 MOA for windage. The same generous spread is available for elevation. At 5.6 ounces, the Romeo 5 adds but little to the weight of the rifle.

Range Testing

Firing the rifle was accomplished with a good supply of ammunition including Federal 62-grain Green Tip, Hornady 55-grain FMJ practice ammunition, Remington 55-grain FMJ, and Hornady 55-grain V-Max. I sighted the rifle in at 25 yards. This was accomplished handily with a minimum of ammunition expanded.

SIG 400 TREAD Specs

Caliber: 5.56 NATO
Weight: 6 pounds, 9 ounces
Overall length: 32.5 inches (stock collapsed); 35.75 inches (stock fully extended)
Receiver: Forged aluminum
Barrel: 16-inch stainless steel, mid-length gas system, 1/8-inch twist
Muzzle Device: SIG 3-­prong flash hider
Stock: Magpul SL-­K
Pistol Grip: SIG
Forend: SIG 15-­inch M-­Lok
Trigger: 7 pounds specified, lighter as tested
Sights: None delivered
Accessories: One 30-­round magazine

The rifle handled well in fast, reactive drills as I engaged man-sized targets at 15 and 25 yards. The SIG Romeo red is fast on target with good features making it an effective combat sight. The rifle handles well with a good balance. I leaned against the bole of a tree and took aim at a 50-yard target.

Firing quickly from this brace, I executed several double-taps. The shots were close together, and after firing five double taps, the X-ring had suffered. Settling down to a solid benchrest firing position, I fired the rifle at 50 yards.

SIG M400 Tread .223/5.56 rifle with a SIG Romeo red dot sight
The author’s personal M400 has proven reliable and accurate.

Firing 3-shot groups, the Federal 62-grain and Hornady 55-grain V-Max tied for top accuracy — just under an inch for three shots. At 100 yards, I fired two 3-shot groups with each load. At this range, the best single effort was 1.5 inches, the average 2.0 inches — good for a red dot equipped AR-15.

At this point my experience is good but not very in depth. I would expect better results with a bit of exploration into ammunition and more acclimation as well. Just the same, I cannot fault accuracy results in any way. The SIG M400 TREAD never failed to feed, chamber, fire, or eject. The rifle is well made of good material and offers SIG quality at a fair price. It should be on anyone’s short list for a front line AR-15 rifle.

When it comes to the AR platform, which are our favorites? How does the SIG M400 Tread compare? Share your answers in the comment section.

  • Pistol grip with a SIG Sauer insignia for an M400 Tread rifle
  • SIG M400 Tread .223/5.56 rifle, black, right profile
  • SIG M400 Tread .223/5.56 rifle, black, left profile
  • SIG M400 Tread .223/5.56 rifle with a SIG Romeo red dot sight
  • Woman resting against an old Ford pickup truck while holding a SIG M400 Tread .223/5.56 rifle
  • multiple shooters shooting and moving between firing stations at a three gun range
  • SIG M400 Tread .223/5.56 rifle, black, right quartering profile
  • Man performing a speed load of the M400 .223/5.56 rifle while running between positions
  • Woman shouldering a SIG M400 with an attached foregrip
  • Three shooters on the firing line with SIG M400 Tread rifles chambered in .223/5.5.6
  • SIG Sauer Romeo 5XDR red dot in the picatinny rail of the SIG M400 Tread rifle in .223/5.56

About the Author:

Bob Campbell

Bob Campbell’s primary qualification is a lifelong love of firearms, writing, and scholarship. He holds a degree in Criminal Justice but is an autodidact in matters important to his readers. Campbell considers unarmed skills the first line of defense and the handgun the last resort. (He gets it honest- his uncle Jerry Campbell is in the Boxer’s Hall of Fame.)

Campbell has authored well over 6,000 articles columns and reviews and fourteen books for major publishers including Gun Digest, Skyhorse and Paladin Press. Campbell served as a peace officer and security professional and has made hundreds of arrests and been injured on the job more than once.

He has written curriculum on the university level, served as a lead missionary, and is desperately in love with Joyce. He is training his grandchildren not to be snowflakes. At an age when many are thinking of retirement, Bob is working a 60-hour week and awaits being taken up in a whirlwind many years in the future.

Published in
Black Belt Magazine
Combat Handguns
Rifle Magazine
Gun Digest
Gun World
Tactical World
SWAT Magazine
American Gunsmith
Gun Tests Magazine
Women and Guns
The Journal Voice of American Law Enforcement
Police Magazine
Law Enforcement Technology
The Firearms Instructor
Tactical World
Concealed Carry Magazine
Concealed Carry Handguns

Books published

Holsters for Combat and Concealed Carry
The 1911 Automatic Pistol
The Handgun in Personal Defense
The Illustrated Guide to Handgun Skills
The Hunter and the Hunted
The Gun Digest Book of Personal Defense
The Gun Digest Book of the 1911
The Gun Digest Book of the 1911 second edition
Dealing with the Great Ammunition Shortage
Commando Gunsmithing
The Ultimate Book of Gunfighting
Preppers Guide to Rifles
Preppers Guide to Shotguns
The Accurate Handgun
The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (10)

  1. THE ARCHITECT, Yes I understand the physics of the pistol length systems cannot fit a mid-length gas tube in a 6″ space, but am glade to hear more companies are going to mid-length on the 16+” systems. As someone who has much degraded hearing, due to maybe poor career choices, while Pistol Caliber Carbines make sense, Rifle Caliber Pistols, seem a poor choice if you value your future hearing capabilities. Most insurance companies do NOT cover hearing aids (like $6,000 for real ones), and just like glasses, hearing aids do NOT replace hearing, they only aid it a best. A 5.56 using a 16+” barrel, and 32db reducing hearing protection still falls outside the safe hearing range, so double plug is really a necessity, and I doubt double hearing protection brings it anywhere close to actual protection when using a 6″ system. Hearing loss is no fun. Speaking from experience.

  2. Yes, I own the Saint and the Tread and have spent a long time comparing , not only those but, almost all AR platforms in the mid range bracket.
    Both have merits. The SA rig I had built up from stock was good out of the box but an improved trigger and different furniture was a must for me. Fore grip (angled) and an trigicon MRO, flared tac lite and eventually an 18” barrel with an SME muzzle.
    All that said, out the box it functioned well and the upper/lower mated well together. Gas needed adjusted but ran good. It’s solid. Bought the Sig many years later and we did a comparison which was a close race with the Sig edging out the SA by just a few points.
    It’s been awhile but I remember in long distance shooting, even with the longer barrel, the Saint holds true to everything the m400 has from ergo to groupings they are comparable. My rig was much heavier with the added goodies so it wasn’t apples to apples.
    I can say with all the upgrades the Saint had , it ran no better than the m400 out of the box after gas adjustments initially.
    Bottom line: if you already have either/or one of them, then no need to get the other if your wanting a dramatic difference. An upgrade would be a Daniel Defense or like. Or you can buy your Tread in 300 BO if your Saint is chambered in 5.56/.223 for fun.

  3. In regards to ‘mid length gas system’.
    There’s a good reason why they do not apply this to every AR they produce. Generally they produce multiple length barrels on the same platform for SBR, Pistol length and rifle length AR’s.
    Mid length is an ideal gas system as overall functionality is improved and allows the platform to accept more brands of ammunition. Lighter to heavier loads function better. But, all of this is contingent on 16+” inch barrels. I’ve had little issues with 18” barreled setups either.
    But that same platform may be sold as a so called pistol with barreled as short as 6” and generally tap and drilling the hole for the gas block at halfway of a short barrel as this would cause malfunctions. Most companies however have switched fully to mid length gas systems on rifle length setups today.

  4. Oh yes, a mid-length gas system. I don’t understand why more manufactures don’t opt for this Mid-length system. Yes, it takes a little longer to cycle, like any of us could really notice, but the real up-side is: Because it gives the action more time to do its job, It has a whole lot less cycling issues, if any. In other words, mid-length systems let you do mag dumps, vs Clear, Rap n Tap exercises.

  5. presently own and use a Springfield Armory Saint – I am looking forward to acquiring a Sig 400. Can anyone give me an unbiased comparison of the two. The Saint has been my first AR platform rifle after shooting for the past 62 years and has been an exhilarating experience as far as style and firearm operation.

  6. Have to LOVE a company who considers us Correct-Handed people by including ambidextrous controls. All those companies who don’t (cheap at any price), I don’t even give a second look, and would never purchase. Just an FYI: When sighting in an AR, if you ZERO it at 50 yards, and I mean adjust until you can put say 50 rounds into the X ring at 50 yards, you will then have a rifle that is basically zeroed from 25 yards all the way out to 200 yards (if you ever need it). At 100 yards it will impact high, equal to the distance of the centerline of the rifle bore, to the centerline of the optic or sight. Like an inch or two. Once you do this, and know you can put 50 rounds dead center at 50 years, it is quite a confidence builder between you and your AR. Using a bipod helps too.

  7. Been a big advocate for the Sig m400’s versatility and price point. I purchased mine for $800 back in 2015 when the M&P sport 2 and Ruger 556 were selling at $599. I could’ve went with one of them but I knew what I wanted and went for it.
    The Tread is excellent for an AR. It’s build quality is the frill you get out of the entire package. The trigger is crisp and the hand guard easy to grip and direct the muzzle. I put a fore grip on mine which helps steer the platform even in CQB situations.
    It’s not a DDM (Daniel Defense) but it is a strong mid grade AR.
    It runs all the candy you feed it and it’s holding up especially well after a couple thousand rounds.
    So accuracy test put it in the middle of the pack of mid grade AR’s and found I could pop steel at 500 which is a rare opportunity where I reside.
    It’s a solid set up.
    They can be found for under $899 sometimes but that price point seems to be disappearing as lower level or bottom shelf AR’s like the aforementioned prices are being jacked up everyday it seems where brands like Radical, ATI and others are running $599-700 easy but of far less build quality.

    Mid grade? I’d take the Sig over the Springfield Armory platform personally.
    It’s an all round battle proven platform. Like the Colt AR, it’ll run solid and for a long time.

  8. Just as Mr. Streeter writes, I also have astigmatism and wear corrective glasses, so all red dot or holographic sights are crystal clear. Without glasses, they appear blurry.

  9. Just purchased a m400 tread a few weeks ago and it has performed flawlessly (not including operator errors). I have been a shooter, reloader all my life but I have never owned an AR. Thought I’d better get one and being a Sig fan thought this would fit the bill and boy does it ever. Shoots and handles fine. Put a Romeo 5 on it but my astigmatism has caused issues so, after trying a friends, I ordered an LPVO. I’m hoping this works like I think it should. Appreciated your article.

  10. I am in total agreement with Bob. I own a Sig 400 Tread with a Romeo red dot and it is a good solid gun! I have the same accuracy from the bench that Bob’s test showed. Great gun at a really great price point.

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