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Most factory ARs leave you with a shopping list. The Sig Sauer M400 SDI X mostly does not. SIG developed this rifle with direct input from the instructors at SIG SAUER Academy, folks who spend more time behind a carbine in a year than most of us do in a decade, and the feature set reflects that kind of trigger time. The lower gives you a truly ambidextrous layout with a bolt catch and release, safety selector, and mag release that all work from either side, plus an ambi charging handle up top. Left-handed shooters get treated like they matter for once, and righties will notice how much cleaner reloads and malfunction drills run when everything is within reach of both hands.
The 16 inch chrome moly barrel carries a 1:7 twist, which stabilizes everything from light 55 grain range ammo up to heavy 77 grain match loads, and the muzzle wears SIG's hybrid flash hider and compensator on standard 1/2×28 threads. The mid-length direct impingement gas system is a real upgrade over the carbine-length setups on older M400s, smoothing out the recoil impulse noticeably. SIG's two-stage Matchlite Duo trigger with its flat blade breaks clean right out of the box, which is not something you can say about most stock AR triggers. The free-float M-LOK handguard uses a steel clamp lockup design that keeps deflection to a minimum, so hanging a light, laser, or bipod off the rails will not walk your zero around.
At 7 pounds with the Magpul SL six-position stock installed, this rifle balances well and handles quickly whether you are working a carbine course, training on the timer, or just burning through a case on a Saturday. The Flat Dark Earth Cerakote finish looks great and holds up to real use. A flat-top Picatinny rail keeps it optics ready, so mount your favorite red dot or LPVO and get to work. One 30-round polymer magazine comes in the box.
Between the ambi controls, upgraded trigger, mid-length gas, and rock-solid handguard, this is the rare AR that does not need a parts order before its first range trip.
Yes, and that is one of the biggest selling points of this rifle. The SDI lower features an ambidextrous bolt catch and release, safety selector, and magazine release, plus an ambi charging handle. Left-handed users can run the rifle exactly like a right-handed shooter would, and everyone benefits during reloads and transition drills.
No, this rifle ships optics ready with no iron sights installed. The full-length Picatinny top rail gives you plenty of real estate for a red dot, LPVO, or magnified scope, and you can add backup irons if you want them. Plan on mounting your preferred optic before your first range trip.
The 1:7 twist is on the faster side, which means it handles heavier bullets very well. It will stabilize everything from common 55 grain range loads up through 69 and 77 grain match ammunition. If you plan to shoot heavier match bullets at distance, this barrel is a great fit.
The SDI X builds on the Tread with several meaningful upgrades. You get fully ambidextrous controls borrowed from SIG's MCX design philosophy, a two-stage Matchlite Duo flat trigger, a mid-length gas system for softer recoil, and a handguard clamp system that reduces deflection when accessories are mounted. This FDE version also wears a Cerakote finish instead of standard anodizing.
| UPC | 798681714469 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | RM400-SDI-16B-FDE |
| Action | |
| ATF Type | RIFLE |
| Barrel Length | 16" |
| Caliber/Gauge | .223 REM/5.56 NATO |
| Capacity | 30 + 1 |
| Color | Flat Dark Earth |
| Length | 33.25'' |
| Magazine Included | 1 x 30-Round |
| Model | |
| Number of Magazines | 1 30 rd. Polymer Mag |
| Package Height | 4.0 |
| Package Width | 11.3 |
| Product Type | Rifle |
| 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 |
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