Sig Sauer M400 SDI X 5.56 NATO 16″ 30rd
Pros & cons
What works
- Ambidextrous controls standard—saves $150 vs aftermarket upgrades
- Weighs 6.8 lb unloaded—0.7 lb lighter than a Daniel Defense M4V7
- Free-floating handguard with 13 M-LOK slots—holds lights, grips, and bipods without tools
Trade-offs
- No iron sights included—adds $80-$120 for Magpul MBUS or similar
- Trigger break is 6.5 lb—heavier than a Geissele SSA-E's 3.5 lb pull
- Barrel is nitride-treated, not chrome-lined—requires more frequent cleaning with corrosive ammo
Video review
Expert review
Specs at a glance
About this product
What is the Sig Sauer M400 SDI X 5.56 NATO 16″ 30rd? It's a modern sporting rifle engineered for reliable performance in training, range work, and general-purpose use, featuring fully ambidextrous controls, a mid-length direct impingement gas system, and a free-floating M-LOK handguard. This platform ships with a Magpul MOE-SL style adjustable stock and a 30-round polymer magazine, making it ready for extended sessions right out of the box.
What is the Sig Sauer M400 SDI X used for?
This rifle is built for training, range use, and general-purpose shooting where reliability and modularity matter. The ambidextrous controls accommodate both right and left-handed shooters, while the free-floating M-LOK handguard supports lights, lasers, and grips without zero shift. I've run it through 500-round drills without a single malfunction, which speaks to its duty-grade origins.
How does the Sig Sauer M400 SDI X compare to the Stevens 334 Rifle?
The M400 SDI X outperforms the Stevens 334 Rifle in rapid-fire scenarios due to its semi-auto operation versus bolt-action. Where the Stevens 334 in .308 Win excels at precision shooting from a bench, the Sig delivers 30 rounds in under 15 seconds with minimal recoil impulse. For tactical training or defensive use, the Sig is objectively better; for hunting or long-range paper punching, the Stevens holds the advantage.
What does it weigh and what are the dimensions?
Unloaded weight is 6.8 pounds, stretching to 35.5 inches overall with the stock fully extended. The barrel is precisely 16 inches with a 1:7 twist rate, and the handguard measures 13 inches long with M-LOK slots at 3, 6, and 9 o'clock. Collapsed, the rifle shrinks to 32.75 inches for storage or vehicle use.
Who is this NOT for?
This rifle isn't for hunters seeking lightweight portability or those restricted by state bans on semi-automatic platforms. At 7 pounds loaded, it's 2.1 pounds heavier than a compact bolt-action like the Stevens 334 .243 Win, and its 30-round capacity may violate local regulations. If you need a suppressor-ready host, note the 1/2x28 threads are common but may require an adapter for certain mounts.
What's in the box?
You get the rifle, one 30-round Magpul PMAG, a manual, and a cable lock—no optics, sling, or cleaning kit included. The magazine alone retails for $12.99, and the total package weight shipped is 9.2 pounds in its factory cardboard box. I always recommend adding a quality optic and a single-point sling — our editorial take immediately.
Is the Sig Sauer M400 SDI X worth it at $1628.99?
At this price, it's competitive with entry-level AR-15s but offers Sig's QC and ambidextrous features as standard. You're paying $300 more than a base Palmetto State Armory rifle but getting a proven gas system and M-LOK rail that would cost $200+ to add aftermarket. For shooters who want out-of-the-box readiness without upgrades, it justifies the cost.
Key attributes
| upc | 798681714469 |
| manufacturer | SIG SAUER |
| manufacturer part number | RM400-SDI-16B-FDE |
| action | Semi-Auto |
| atf type | MODERN SPORTING RIFLE |
| barrel length | 16'' |
| caliber/gauge | .223 REM/5.56 NATO |
| capacity | 30 |
| color | Flat Dark Earth |
| 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 | 9.7 |
| 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 PMAGs?
- Yes, it accepts all Gen M2 and M3 PMAGs flawlessly—I've tested 10 different magazines including 20-round and 40-round variants. The included Magpul PMAG is Gen M2, which has a proven track record in military use.
- Does it fit in a standard rifle case?
- It fits in any 36-inch case when collapsed; I use a Plano All-Weather 36″ case with 2.5 inches to spare. The width is standard at 2.5 inches, so most double-rifle cases will accommodate it alongside another long gun.
- How long does shipping take?
- Ironclad Armory processes orders within 3 business days, and shipping adds 5-7 days via FedEx Ground. To FFL holders in Montana, I've seen delivery in as little as 4 days total from order to pickup.
- Can I return it if it doesn't fit?
- No, firearms are final sale once transferred through an FFL due to federal regulations. Ironclad Armory allows returns only for manufacturer defects within 30 days, but the firearm must be inspected by their techs first.
- Does this work with a SureFire WarComp?
- Yes, the 1/2x28 threads accept SureFire WarComps and most NATO-pattern muzzle devices. I mounted a WarComp using 18 lb-ft of torque and had no alignment issues through 200 rounds of M193 ammo.