Sig Sauer M400 TREAD 5.56 NATO Semi-Automatic Rifle with 16" Stainless Barrel & 15" M-LOK Handguard
The Sig Sauer M400 TREAD blends the proven AR-15 platform with purpose-built features from Sig’s modular TREAD series. A 16" 416R stainless steel barrel, free-floating 15" M-LOK handguard, and ambidextrous controls make this rifle a ready companion for range, duty, or competition. Recent Newington, NH production (serial prefix 20L) ensures current manufacturing standards, while the factory-installed 3-prong flash hider and polished single-stage trigger add practical value straight from the box.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
The rifle shows light handling wear with a few small surface scratches visible on the finish.
Bore Condition: Excellent – Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling – Sharp lands and grooves.
What’s Included
- 1x 30-round aluminum STANAG-pattern magazine
- SIG SAUER flip-up polymer front and rear sights (installed)
This M400 TREAD is built on forged 7075-T6 aluminum receivers finished in durable black anodizing. A full-length Picatinny rail allows quick mounting of optics or accessories, and the free-float 15" TREAD handguard offers abundant M-LOK slots plus an integral QD sling socket.
The 16" 416R stainless barrel uses a 1:8" right-hand twist optimized for common 55–77 grain bullets. Its mid-length gas system softens recoil impulse, and the muzzle is threaded 1/2x28 TPI with a factory SIG 3-prong flash hider installed.
Controls are shooter-friendly: an ambidextrous safety selector, polished single-stage trigger, and SIG polymer grip come standard. The lower receiver also includes a QD sling socket for quick sling attachment.
Unlike many adjustable AR stocks, this rifle wears a fixed polymer stock, delivering a solid cheek weld and straightforward durability without moving parts.
Part of Sig’s broader TREAD ecosystem, this rifle accepts a wide range of Sig-branded TREAD accessories for future customization, yet arrives fully capable right out of the box.