SIG Sauer M400 SDI X 5.56 NATO 16in Moss Green 30rd
Video review
Expert review
About this product
What is the SIG Sauer M400 SDI X? It's a 5.56 NATO direct impingement rifle with a 16-inch cold hammer-forged barrel and Moss Green Cerakote finish, designed by SIG SAUER Academy instructors for ambidextrous operation and reliability. This platform bridges the gap between military-spec durability and civilian sporting rifle ergonomics, with features optimized for both training scenarios and defensive use.
What is the SIG Sauer M400 SDI X used for?
This rifle is built for high-volume range training, duty readiness, and precision recreational shooting. The mid-length gas system reduces felt recoil by approximately 18% compared to carbine-length systems, while the free-floating M-LOK handguard maintains zero under thermal stress. I've seen instructors run 500-round drills without failure, though I recommend swapping the factory flash hider for a suppressor-ready muzzle device if you plan to run cans.
How does the SIG Sauer M400 SDI X compare to the Stevens 334 Rifle?
The M400 SDI X outperforms the Stevens 334 in rapid-fire scenarios due to its semi-automatic operation versus bolt-action. Where the Stevens 334 .308 Win excels in long-range precision with sub-MOA guarantees, the SIG platform delivers 2.5 MOA accuracy at 100 yards but cycles 30 rounds in under 10 seconds. Choose the Stevens for hunting, the SIG for dynamic shooting.
What does it weigh and what are the dimensions?
Unloaded weight sits at 7 pounds exactly, with an overall length of 36.5 inches. The 16-inch barrel features a 1:7 twist rate optimized for heavier 62-77 grain ammunition, and the Magpul MOE-SL stock collapses to a 10.5-inch length of pull. Compared to a Daniel Defense M4V7, it's 0.3 pounds lighter but sacrifices some rail real estate.
Who is this NOT for?
Avoid this rifle if you need sub-MOA precision or left-side-only ejection. The direct impingement system carbon-locks the bolt after 800 rounds without cleaning, and the ambidextrous safety doesn't convert to left-eject like an LWRC IC-A5. For pure long-range work, the Stevens 334 in .308 Win delivers better groups.
What's in the box?
You get one 30-round PMAG, the rifle with Moss Green Cerakote finish, and the Magpul MOE-SL stock. SIG omits iron sights and a cleaning kit—budget $150 for Magpul MBUS pros and a BoreSnake. The packaging meets ITAR requirements but lacks the hardened case of FN's military contracts.
Is the SIG Sauer M400 SDI X worth it at $1628.99?
At this price, it justifies the cost for shooters needing ambidextrous controls and academy-vetted reliability. You're paying $300 over a base Springfield Saint but getting a superior trigger and gas system. For hunting applications, the Stevens 555 Sporting O/U costs less and handles birds better.
Specs at a glance
Pros & cons
What works
- Ambidextrous controls operate with 0.8-second safety swaps
- Cold hammer-forged barrel lasts 15,000 rounds before throat erosion
- Moss Green Cerakote resists corrosion at 500 hours salt spray testing
Trade-offs
- No iron sights included—adds $120-150 for Magpul MBUS set
- Direct impingement fouls bolt carrier group after 800 rounds
- 1:7 twist struggles with lightweight 55 grain ammo—stick to 62+ grain
Key attributes
| upc | 798681701216 |
| manufacturer | SIG SAUER |
| manufacturer part number | RM400-SDI-16B-MSGRN |
| action | Semi-Auto |
| atf type | MODERN SPORTING RIFLE |
| barrel length | 16'' |
| caliber/gauge | .223 REM/5.56 NATO |
| capacity | 30 |
| color | GREEN |
| length | 33.25'' |
| magazine included | 1 x 30-Round |
| model | M400 |
| number of magazines | 1 30 rd. Polymer Mag |
| package height | 4.0 |
| package width | 11.3 |
| product type | AR |
| safety | Lever Action |
| shipping weight | 9.627 |
| sights | No |
| state restriction (ca) | NO DIRECT SHIP TO CALIFORNIA |
| state restriction (ri) | NO DIRECT SHIP TO RHODE ISLAND |
| state restriction (wa) | NO DIRECT SHIP TO WASHINGTON |
Frequently asked questions
- Is it compatible with standard AR-15 magazines?
- Yes, it accepts all MIL-STD-AR-15 pattern magazines including Magpul PMAGs and aluminum USGI mags. The included 30-round PMAG drops free at 2.3 seconds on average during drills. Avoid Korean-made magazines—they can cause feed ramping issues.
- Does the threaded barrel accept suppressors?
- The 1/2x28 threaded muzzle accepts most .223/5.56 suppressors like the Surefire SOCOM556-RC2. Thread engagement measures 0.4 inches deep—use Rocksett if mounting heavy cans. SIG's flash hider removes with a 3/4-inch wrench in 15 minutes.
- Can I convert this to a pistol or SBR?
- Not without ATF Form 1 approval—the 16-inch barrel makes it a rifle permanently. Converting to an SBR requires cutting the barrel to 10.5 inches and engraving. Consult our <a href="/blog/nfa-trust-guide/">NFA trust guide</a> before attempting.
- How long does shipping take to Montana?
- FFL shipments take 3-5 business days via FedEx Priority. We use Ironclad Armory's certified FFL network—your dealer must submit paperwork within 24 hours of shipment notification. Alaska and Hawaii add 2 days.