Description

Upgrade your M4/AR rifle or lower assembly with this complete, drop-in M400 upper assembly. This kit includes all the necessary components for a complete swap, including a two-stage match trigger as well as the popular TANGO-MSR LPVO 1-6X24 (SFP) riflescope. The free-floating handguard utilizes a new steel lockup design that significantly reduces handguard deflection by providing maximum rigidity and allows for accessories to be attached on all four sides with no effect on accuracy. The 2-Stage Matchlite Duo trigger provides an out-of-the-box crisp 4.5 - 6.5lb pull weight with a flat blade design for a precision feel. Together, this kit gives you the one-stop solution when it comes to taking your M4/AR to the next level.

The M400 was developed with the input from the professional instructors at SIG SAUER Academy. Building upon their decades of experience and countless hours of instruction, we have developed the M400 to meet the highest standards of performance and reliability.

INCLUDES:

– (1) Complete 16" 5.56 NATO Upper Assembly
– (1) SIG 2-Stage Matchlite Duo Trigger
– (1) TANGO-MSR LPVO 1-6X24MM (SFP)
– 16" 5.56NATO M400 UPPER ASSEMBLY FEATURES INCLUDE:

FEATURES:

– Black Anodized Finish
– 3-prong flash-hider accept our SLH & SLX suppressor systems.
– Dual Clamp Handguard Locking System for Reduced Deflection
– Low-Profile Gas Block with Mid-Length Gas System
– High-quality, premium barrel
– TANGO-MSR LVPO 1-6X24MM FEATURES:

– High-performance 6x optical system with low-dispersion glass
– Integrated thread-in throw leaver for quick magnification changes
– Illuminated MSR BDC-6 reticle with 11x brightness levels
– Lay flat flip-back lens covers included
– Dependable waterproof, shockproof, and fog-proof performance
– Includes ALPHA-MSR one-piece aluminum cantilever mount

SPECIFICATIONS:

– SKU UAM400-SDI-16B-P-TM6
– Model SIGM400
– Barrel Extension M400
– Barrel Length 16 in [406.4 mm]
– Bolt Carrier Finish FNC
– Bolt Carrier Group Included Yes
– Caliber 5.56 NATO
– Chrome Lined Barrel No
– Charging Handle Included Yes
– Color Black
– Forward Assist Yes
– Free Floated Handguard Yes
– Gas System Length Mid Length
– Handguard Length (in.) 15
– Handguard Inside Diameter 1.25-in
– Handguard Material Aluminum
– Muzzle Device 3-Prong/SIG Suppressor QD
– Muzzle Thread Pitch 1/2-28
– Operating System Gas
– Receiver Finish Black Anodized
– Twist Rate 1:7

Explore more Sig Sauer Uppers gun parts.

Rebates for Sig Sauer brand

Exp. date: 01.09.2026
Buy a New Applicable SIG SAUER Handgun Between 06/01/26 and 08/31/26, Receive One (1) SIG SAUER FOXTROT-EDC COMPACT Flashlight. (SKU: SOFEC002)
*Purchases of all SIG SAUER P365, P320, M17-M18, P210, P211, P220, P226, P229 and 1911 models are included in this offer. All other SIG SAUER Handguns are excluded from this promotion.