The M400 Forge is SIG's answer to the question of what an AR-15 should come with from the factory. Rather than a stripped mil-spec rifle you immediately start upgrading, the Forge ships with a TriggerTech 3.5-pound two-stage flat trigger, a cold hammer forged 16" barrel, a full-length free-floating M-LOK handguard, a Magpul SL-K stock, ambidextrous safety, and a ROMEO-MSR Gen II red dot already in the box. Part number RM400-556N-16B-FORGE-10, UPC 798681744121.

The Trigger Is the Story

Most factory AR-15s ship with a gritty single-stage mil-spec trigger that shooters replace within a month. The Forge comes with a TriggerTech 3.5-pound two-stage flat-blade trigger — a genuine aftermarket-grade unit, installed at the factory. That alone changes what the rifle is capable of on paper targets and at distance.

Cold Hammer Forged, Mid-Length Gas

The 16" barrel is cold hammer forged steel with a 1:7 twist — the twist rate that stabilizes heavy match and defensive bullets as well as light varmint loads. It runs a mid-length direct impingement gas system, which softens the recoil impulse and reduces bolt velocity compared to a carbine-length system on a 16" barrel. Threads are 1/2x28 with a 90-degree shoulder, wearing an A2 birdcage flash hider.

Furniture and Controls

• Magpul SL-K 6-position stock — slim, light, and adjustable.
• Reduced-angle grip for a more natural wrist position behind a modern rifle.
• Ambidextrous manual safety.
• Black anodized alloy M-LOK forend, free-floating, with a full-length Picatinny top rail.
• Black anodized receiver finish throughout.

Included ROMEO-MSR Gen II Red Dot

The bundled optic is a genuine SIG ROMEO-MSR Gen II, not a placeholder:

Note: the ROMEO-MSR Gen II does not feature MOTAC motion-activated illumination, so turn the sight off before long-term storage.

SIG M400 Forge Specifications

Who This Rifle Is For

First-time AR buyers who want to skip the upgrade cycle, and experienced shooters who recognize that a factory TriggerTech and a cold hammer forged barrel would cost most of the rifle's difference in price if bought separately. The 10-round magazine configuration makes it saleable in capacity-restricted jurisdictions.

Frequently Asked Questions

Does the red dot really come with it?

Yes. The ROMEO-MSR Gen II with a 2 MOA dot is factory-included on the Forge.

Does the optic have shake-awake?

No. SIG explicitly states the ROMEO-MSR Gen II does not have MOTAC. Turn it off before storing the rifle.

Why only a 10-round magazine?

This is the 10-round configuration, intended for capacity-restricted states. SIG offers the same rifle with a 30-round magazine under a different SKU, along with Concrete Gray, FDE, and Moss Green variants.

Mid-length or carbine gas?

Mid-length — a smoother impulse and lower bolt velocity than carbine gas on a 16" barrel.