TFB Review: SIG Sauer’s NEW M400 TREAD pistol

    Tread with a smaller footprint:

    SIG Sauer has just released a new iteration of their TREAD line of 5.56 AR’s, this time in an 11.5″ barreled pistol configuration.  TFB was lucky enough to briefly get our hands on one of these pistols for a quick review.

    Per SIG:

    The M400 TREAD pistol is an optics ready, aluminum framed pistol. The TREAD pistol is equipped with an 11.5” nitride coated, cold hammer-forged barrel, with a free-floating M-LOK handguard, a single-stage polished/hard-coat trigger, ambidextrous controls, a KAK Industry Shockwave Blade 2.0 brace, a carbine-length gas system, and is available in 5.56 NATO.

    Existing TREAD accessories are compatible with the M400 TREAD Pistol, with the exception of the M-LOK handguards in the 13” and 15” lengths, a lightened accessory handguard built for the TREAD pistol will be available in 10.5” length. The TREAD accessories include: a 3-chamber compensator; an ambidextrous charging handle made of aircraft grade aluminum and dual roll pin design; a ROMEO5 optic featuring a 2MOA dot with ten illumination settings, MOTAC, and 50k hour battery life; flip-up front and rear iron sights that are easy to install, adjustable, and deploy quickly; an M-LOK front sight adapter with co-witness height made of lightweight aluminum; multiple configurations of M-LOK grip kits made of high-strength polymer; and a factory upgraded 2-stage trigger.


    M400 TREAD Pistol Specs:

    Total Length: 27” Barrel Length: 11.5” Weight (incl. magazine): 6lbs
    Height: 7.5” Width: 2.5” Barrel Twist: 1:7”


    MSRP: $951.00


    M400 TREAD Branded Accessories Specs (all prices MSRP):

    M-LOK Handguard 10.5” $149.00
    ROMEO5 Optic $179.00
    Adjustable Flip-Up Sights $149.00
    2-Stage Match Trigger $119.00
    Ambidextrous Charging Handle $49.00
    3-Chamber Compensator $49.00
    M-LOK Front Sight Adapter $29.00
    M-LOK Hand Stop Kit $29.00


    The M400 TREAD pistol and TREAD accessories are available in retail stores. The full-line of TREAD accessories and TREAD branded apparel can also be purchased at

    Get Social: follow SIG SAUER on Facebook, Twitter, Instagram, and YouTube for the latest news, product announcements, events, and updates.

    Initial impressions:

    The M400 TREAD pistol ships in a cardboard box, with one 30-round Magpul PMAG.  Upon lifting it out of the box, I appreciated the slick squarish M-Lok handguard.  No cheese grater here like on my old P516 pistol.  The tread upper has a Brass Aluminum forge marking, vs the Cerro marking on my old P516. (Author’s note: my old gun was previously erroneously referred to as the M400-some readers were kind enough to point out the old piston driven guns were all 516’s)

    Top is old P516 piston pistol, bottom is TREAD DI pistol

    The lower has a few differences as well.  The TREAD pistol features an adjustable KAK Shockwave Blade brace vs the non-adjustable SigTac brace on the old P516.  The trigger pull of the single-stage hard-coat polished trigger had a crisp break with no creep.  The reset was positive and short.  The trigger is on the heavier side, however, averaging out at 6 lb, 4oz.  Total weight of the pistol was 6lb, 4.7oz including the mounted Romeo5 RDS.  Without the Romeo5, it is a full pound lighter than the old P516 pistol I have, a significant improvement in weight.

    The same ambidextrous magazine release has been retained from the old pistols, along with ambidextrous rear QD stud holes and an ambidextrous selector switch.  The right-hand side of the sector switch is nicely truncated so as to not dig into the hand of a right-handed shooter.   The ambidextrous QD studs preclude the use of certain collapsible arm braces such as Maxim Defense CQB, as they protrude in the way.

    QD stud blister on the lower

    I have mixed feelings about the TREAD grip panels that came attached to the handguard.  On one hand, they did provide a more positive purchase on the firearm.  On the other hand, I found the yellow background color to be rather glaring and garish.  Upper to lower receiver fit was rather good, aided further by a wedge in the rear of the lower receiver.

    Range Results


    I took the TREAD pistol out to the range with 200 rounds of SIG Elite 55gr FMJ graciously provided by SIG, as well as some other light ball, M855, and heavy match ammo.  Initial rapid fire results at 25 yards were good.  The pistol ripped through a 60 round Magpul drum with no issues and demonstrated decent offhand accuracy.  This author was able to keep everything within IPSC A zones on the torso and head while being shot from a number of dynamic positions.  The Romeo5 RDS was mounted at the appropriate height and was intuitive and easy to use.

    Moving on to 50 yards, the 11.5″: CHF barrel posted decent results.  I first shot for accuracy with a front and rear rest.  The very best 5 shot group with SIG’s 55gr FMJ ammunition was .32″, but the average was .81″.  Trying again with a smoking hot barrel (after 300 rapid fire rounds) the groups opened up to 1.98″.  Decent accuracy with a thin barrel after so many rounds.

    Moving out to 100y and beyond, I began to see the limitations of the TREAD pistol.  Groups across the board averaged roughly 2″ with the following ammo:

    • Sig Elite 55gr FMJ
    • PMC 55gr FMJ
    • IWI M855 62gr
    • Black Hills 68gr HP
    • Black Hills 77gr OTM

    The best performance at 100y came from Black Hills’ 75gr HP, coming in at 1.85″.  These accuracy results are very competitive with other AR pistols in this price range.  Trying to achieve repeatable hits at 300y, however, was quite difficult.  This is not a short-barreled AR that one can smack 500y steel with like some other platforms I have used.


    Velocities were measured with a Labradar with 55gr and 77gr loads, 10 shots each for an average representation of light and heavy loads.

    SIG Sauer 55gr FMJ average MV 2586fps, V @ 50y 2491fps (V @ 100 missing due to chronograph having difficulty tracking projectile at that range)

    Black Hills 77gr OTM average MV 2503fps, V @ 50y 2401fps, V @ 100y 2305fps


    The TREAD and the D60 got along just fine

    The M400 TREAD pistol was shot primarily in hot and very dusty conditions.  Right out of the box without any cleaning or additional lubrication, it performed flawlessly throughout 600 rounds fired from a multitude of different kinds of magazines.  These included Gen 1, 2, and 3 PMAGs, a D60 drum, magazines from HK, C Products, Brownells and even an old Colt 20 rounder from the 1970s.

    a smattering of mags and ammo

    the TREAD pistol burned through plenty of ammo without a problem

    The pistol was fired sideways, upside down, supported and unsupported with nary a hiccup.  It churned through 300 straight rounds as fast as I could pull the trigger and change magazines.  Though the barrel was smoking and the handguard would have been too hot to handle without gloves, it did not malfunction at all.  I have seen AR platform guns that cost 3-4 times as much not perform as well.

    Overall impressions:

    Objectively, the SIG Sauer M400 TREAD Pistol was 100% reliable during TFB’s short assessment period.  Accuracy at “pistol” ranges out to 50y was very good, even after the barrel got smoking hot.  It is a much lighter package than the old P516 piston-driven pistol, and handling reflects the reduction in weight.

    Subjectively, this author found the TREAD pistol to be a decent value for the price point.  Its strongest points are reliability, compactness and light weight.  With a short barrel, one must be very careful about ammunition selection, however.  If one is considering this pistol, something like Black Hill’s 5.56 50gr TSX or Hornady’s 55gr FTX would be worth a look. While there are more accurate AR pistol platforms out there, they typically cost 2-3 times more.  The M400 TREAD pistol is a solid choice for a low-cost entry into the AR pistol world for a decent truck or ruck gun.

    Though the trigger is a bit on the heavy side and accuracy wanes at longer ranges, it would be a decent truck gun for those who don’t have the inclination to assemble their own pistol.  This author thinks that with the M400 TREAD, SIG Sauer has given the SAINT pistol series some serious competition at a lower price.


    • Light Weight
    • Reliable
    • Slick
    • Adjustable Brace
    • Good Value “truck gun” for the Price


    • Accuracy at longer ranges is a bit lacking
    • Trigger pull is a bit on the heavy side
    • QD stud holes at the sides of the lower preclude use of some collapsing braces

    For more information, please visit SIG Sauer.

    Thanks to HSS Idaho for technical support and range time

    Rusty S.

    Having always had a passion for firearms, Rusty S. has had experience in gunsmithing, firearms retail, hunting, competitive shooting, range construction, as an IDPA certified range safety officer and a certified instructor. He has received military, law enforcement, and private training in the use of firearms. He is fortunate enough to have access to class 3 weaponry as well.