SIG Sauer M400: A Top-Selling Semi-Auto Carbine

SIG Sauer’s M400 was the company’s first AR-15-style carbine. It caught enthusiasts largely by surprise at its introduction—roughly a decade ago—but it quickly became a popular choice in a market teaming with modern sporting rifles. The direct-gas impingement firearm was one of the top-selling semi-automatic rifles last year, thanks partly to its budget-friendly price point. The quality build and variety of upgrades over the original likely played a bigger role, though.

Today M400 models are part of SIG Sauer’s Tread line, which was introduced on Oct. 1, 2018. There are three versions available—the SIGM400 Tread, SIGM400 Tread Coil and SIGM400 Tread Predator. There’s also a fourth, but it’s a pistol variant (SIGM400 Tread Pistol).

All are chambered in 5.56x45 mm NATO, come with ambidextrous fire controls and a three-prong flash hider. Gas blocks are micro and mid-length. Their free-floating barrels are made from stainless steel and feature an M-LOK compatible aluminum handguard. Most come with a six-position Magpul SL-K stock, with state-complaint versions being the exception. Receivers have a Picatinny rail for optic mounting, barrels are 16” long and feature 1:8” rifling.  

Versions include the Predator version (seen above), which is new for 2021. It comes with a five-round polymer magazine and a precision stock adjustable for comb height and length-of-pull. The gun wears a Cerakote Elite Jungle finish, 15” M-LOK Predator handguard and weighs in at 7.5 lbs.

At 7 lbs. and 30.8” in length, the Coil models comes with a ROMEO5 red-dot sight installed, flat-blade Enhanced Trigger, fore-end pistol grip and 13” lightweight handguard. The SIGM400 Tread is the baseline model. Each ship with 30-round magazines—10 rounders for restrictive states.

Last year the SIGM400 ranked fourth on Gunbroker.com’s annual list of top-selling semi-automatic rifles. The position is determined by volume of purchases through FFLs using the services of the website.

SIG Sauer doesn’t list MSRPs on its website, probably a wise decision considering the current demand. However, prices at many major retailers are hovering somewhere around $1,000 depending on model.