SIG M400
- Category
- Carbine
- Barrel
- 406 mm
- Weight, empty
- 3.20 kg
- Introduced
- 2011
About
What it is, and why it matters
The SIG M400 (SIGM400) is an American direct-impingement, gas-operated, semi-automatic carbine chambered in 5.56x45mm NATO. Built on the AR-15 platform by SIG Sauer, it pairs forged 7075-T6 aluminum upper and lower receivers with a 16-inch chrome-lined barrel and a 1:7 right-hand twist. Standard features include a flared magazine well, ambidextrous magazine release, M1913 Picatinny rails, adjustable iron sights, quick-detach sling points, and a collapsible stock. Introduced as SIG Sauer's flagship modern sporting rifle, it later spawned the popular M400 TREAD and M400 Forge variants.
The M400 was SIG Sauer's entry into the crowded AR-15 modern sporting rifle market, leveraging the company's manufacturing base in Exeter, New Hampshire. Its TREAD sub-line, named for the company's 'Free Yourself' branding, became one of the most commercially successful budget-tier AR-15 carbines in the United States.
The base M400 accepts standard AR-15/M16 magazines and uses an M4-style feed ramp. An extractor support pin guards against over-pressure conditions.
Specification
Everything measured
IdentityWhat it is, who built it and when.
- Manufacturer
- SIG Sauer
- Category
- Carbine
- Country
- United States
- Status
- In production
- Produced
- 2011
DimensionsAs issued, without a magazine or an optic.
- Barrel
- 406 mm
- Overall length
- 902 mm
- Weight, empty
- 3.20 kg
ActionHow it cycles, what trips it, and what feeds it.
- Action
- Gas operated
- Firing mechanism
- Hammer fired
- Trigger
- Single action
- Capacity
- 30
- Magazine
- Detachable box
MaterialsEach swatch is the material itself, not a colour chosen to stand for it.
- Frame
- Aluminum
- Barrel
- Steel
- Stock
- Polymer
- Finish
- Hard coat anodized
BallisticsFrom the service cartridge, not a handload.
- Muzzle velocity
- 940 m/s
- Muzzle energy
- 1767 J
- Effective range
- 500 m
Trajectory
What the round does downrange
Solved from the muzzle figures and the bullet. The dashed rule is the effective range on the record, and the crosses are the steps the solver returned.
Features
What it has
What the record lists as fitted, drawn from the catalogue.
Direct impingement gas system
Chrome lined barrel
Forged 7075 t6 aluminum receivers
Ambidextrous magazine release
Flared magazine well
Picatinny rail
Adjustable iron sights
Quick detach sling points
Collapsible stock
Standing
How it compares
Each figure against the firearms of the same type and cartridge that record it, or of the same type where that cartridge has too few. Positions are read to the nearest tenth.
| Measurement | This firearm | Median | Position |
|---|---|---|---|
| Empty weightAmong 141 5.56x45mm NATO carbines | 3.20 kg | 2.95 kg | Heavier than about 80% |
| Overall lengthAmong 144 5.56x45mm NATO carbines | 902 mm | 838 mm | Longer than about 80% |
| Barrel lengthAmong 150 5.56x45mm NATO carbines | 406 mm | 406 mm | Longer than about 70% |
| Magazine capacityAmong 150 5.56x45mm NATO carbines | 30 | 30 | Near the median |
Answers
Questions about the SIG M400
How much does the SIG M400 weigh?
The SIG M400 weighs 3.20 kg (7.06 lb) empty.
What caliber is the SIG M400?
The SIG M400 is chambered in 5.56x45mm NATO.
How many rounds does the SIG M400 hold?
The SIG M400 holds 30 rounds, fed from a detachable box magazine.
How long is the SIG M400?
The SIG M400 is 902 mm (35.5 in) long overall, with a 406 mm (16.0 in) barrel.
Who makes the SIG M400?
The SIG M400 is made by SIG Sauer (Germany). It was designed by SIG Sauer.
When was the SIG M400 introduced?
The SIG M400 was introduced in 2011.
How does the SIG M400 operate?
The SIG M400 uses a gas operated action, and its firing mechanism is hammer fired.
Compatibility
Which parts fit this firearm
Studio
Every part that mounts on this, resolved
Not a list the maker typed out: the answer comes from the mounts this firearm exposes and the interface each part needs, so it stays right when either one changes.
- Every part that mounts on any firearm in the catalogue
- Interface standards, platforms and fit overrides
- The same answers through the API and the MCP server
Requires a signed-in GunSpec account on the Studio plan. The answer is computed per part, so it is not part of the public record.
Provenance
What the record holds
Every figure above was taken from one of these pages. The confidence reflects how much of the record came from a page a claim can be checked against.
In service
- Civilian sport shooters
- United States
- United States law enforcement agencies
- United States
Provenance
Confidence in this record
85%
Stockists
Where to buy
Offers link straight to the shop. GunSpec never takes the order.
No shop has listed this firearm yet
Stock and prices come from the shops themselves. If you sell this firearm, you can list it and it appears here.
List a firearmMCP
Ask an assistant about it
The same record, reached the way a person asks for it rather than the way a program does.
Ask GunSpec
Works with
Point an MCP client at GunSpec and it answers from the catalogue rather than from memory. A free key covers the read tools.
API
The call that returns this record
The same fields, in the same units, from the same endpoint the page reads.
curl --request GET \ --url 'https://api.gunspec.io/v1/firearms/sig-m400' \ --header 'X-API-Key: your_key'{ "id": "sig-m400", "name": "SIG M400", "manufacturer": { "id": "sig-sauer", "name": "SIG Sauer", "countryCode": "DE", "foundedYear": 1985, "website": "https://www.sigsauer.com", "logoUrl": null, "description": null, "status": null, "defunctYear": null, "stateOwned": null, "makesFirearms": null, "parentId": null, "predecessorId": null, "createdAt": "2026-02-11 23:44:40", "updatedAt": "2026-02-18 03:40:48", "version": "944f4088befdcee3b0aa7caf122998351ef3d78abc525a2bdec9df81e65a6b30" }, "category": { "id": "carbine", "name": "Carbine", "description": "Shortened rifles for close-quarters use" }, "country_of_origin": "US", "year_introduced": 2011, "barrel_length_mm": 406, "weight_empty_g": 3203, "action_type": "gas_operated"}