Sig Sauer M400 5.56 NATO AR-15 Rifle, 16 in Threaded Barrel, Free-Float DSI Handguard, 30+1
This Sig Sauer M400 stands out as a direct-impingement AR-15 platform rifle in 5.56 NATO with a 16-inch threaded steel barrel and an aftermarket DSI-marked free-float aluminum handguard. It features a flat-top upper with a T-marked MIL-STD-1913 rail, forward assist, and ejection-port cover, plus a three-prong flash hider. Marked with SIG Sauer Newington, NH receiver rollmarks, it includes a 6-position collapsible stock and SIG polymer pistol grip, and ships with a 30-round PMAG.
Condition
Overall Condition: Good condition, showing some signs of prior use and handling.
Bore Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: There are handling and use marks on exterior surfaces. Please review the photos for a close look at these areas.
What’s Included
- SIG Sauer M400 Owner's Manual
- 1 Magpul PMAG Gen M3 30-round magazine for 5.56x45
Built on the AR-15 platform, this M400 uses a direct-impingement gas system with a low-profile gas block concealed under a slim, octagonal DSI-marked free-float handguard. The handguard clamps at the barrel nut with multiple cross screws and is slick-top for a streamlined feel.
The 16-inch steel barrel is threaded and capped with a three-prong flash hider over a crush washer. This setup supports accessory compatibility at the muzzle and maintains a balanced profile for general-use 5.56 NATO shooting.
The flat-top upper carries a T-marked MIL-STD-1913 rail, and includes a forward assist and ejection-port dust cover. Controls are non-ambidextrous with a standard right-side magazine release and a manual safety selector.
Furniture includes a 6-position collapsible polymer stock and a SIG SAUER polymer pistol grip. The rifle accepts AR-15 pattern magazines and has a 30+1 capacity with 5.56 NATO or .223 Remington.
Receiver construction is aluminum with a hard-anodized finish. Markings include "SIG SAUER SIGM400" on the upper and "SIG SAUER INC NEWINGTON, NH, USA" with the circular SIG logo on the lower magwell.