SIG MCX Rattler
- Category
- Personal Defense Weapon
- Barrel
- 140 mm
- Weight, empty
- 2.31 kg
- Introduced
- 2018
About
What it is, and why it matters
The SIG MCX Rattler is an ultra-compact personal defense weapon developed from SIG Sauer's MCX rifle family, built around a short-stroke gas piston operating system and a 5.5-inch barrel. Designed primarily around .300 AAC Blackout to deliver carbine-class terminal performance from a sub-machine-gun-sized envelope, it bridges the gap between SMG and rifle. The platform uses standard AR-15 magazines and parts compatibility, with a side-folding Pivoting Contour Brace (PCB) that collapses the weapon to roughly 432 mm (17 in). In May 2022 USSOCOM awarded SIG a sole-source five-year Commercial PDW contract, citing SIG as the only vendor that could meet the requirement.
Born from a 2017 USSOCOM search for a sub-MP5-sized PDW, the Rattler folds to just 432 mm - small enough to vanish under a low-profile jacket - yet fires intermediate-rifle-class .300 BLK. SOCOM's own justification stated SIG was 'the only vendor that can fulfill USSOCOM's need,' making it the first-ever sole-source SOCOM PDW contract.
Often confused with the larger MCX-SPEAR (basis for the US Army XM7/M7 NGSW rifle) - these are separate platforms in different size and caliber classes. Rifling twist of 1:5 (127 mm) is unusually fast, optimized for stabilizing heavy 220 gr subsonic .300 BLK projectiles. Civilian variants are semi-automatic only; SOCOM CPDW variant is select-fire. Rattler LT (2022+) introduced lighter chassis with longer barrel options (171 mm / 197 mm) and 7.62x39mm chambering option.
Specification
Everything measured
IdentityWhat it is, who built it and when.
- Manufacturer
- SIG Sauer
- Category
- Personal Defense Weapon
- Country
- United States
- Status
- In production
- Produced
- 2018
- Variant of
- Compact pdw
DimensionsAs issued, without a magazine or an optic.
- Barrel
- 140 mm
- Overall length
- 584 mm
- Height
- 203 mm
- Width
- 71 mm
- Weight, empty
- 2.31 kg
- Weight, loaded
- 2.70 kg
ActionHow it cycles, what trips it, and what feeds it.
- Action
- Gas operated short stroke piston
- Firing mechanism
- Hammer fired
- Trigger
- Single stage
- 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
- Black hardcoat anodized
BallisticsFrom the service cartridge, not a handload.
- Muzzle velocity
- 625 m/s
- Muzzle energy
- 1585 J
- Effective range
- 200 m
- Maximum range
- 460 m
- Rate of fire
- 750 rpm
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.
Short stroke gas piston
Rotating bolt
Two position adjustable gas regulator
Side folding pivoting contour brace
Quick change barrel
Ambidextrous controls
Full length picatinny top rail
M lok handguard
Ar15 magazine compatible
Suppressor ready 5 8 24 threads
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 54 personal defense weapons | 2.31 kg | 2.23 kg | Near the median |
| Overall lengthAmong 53 personal defense weapons | 584 mm | 582 mm | Near the median |
| Barrel lengthAmong 55 personal defense weapons | 140 mm | 168 mm | Shorter than about 70% |
| Magazine capacityAmong 57 personal defense weapons | 30 | 30 | Holds more rounds than about 70% |
Answers
Questions about the SIG MCX Rattler
How much does the SIG MCX Rattler weigh?
The SIG MCX Rattler weighs 2.31 kg (5.10 lb) empty and 2.70 kg (5.95 lb) loaded.
What caliber is the SIG MCX Rattler?
The SIG MCX Rattler is chambered in .300 AAC Blackout and 5.56x45mm NATO.
How many rounds does the SIG MCX Rattler hold?
The SIG MCX Rattler holds 30 rounds, fed from a detachable box magazine.
How long is the SIG MCX Rattler?
The SIG MCX Rattler is 584 mm (23.0 in) long overall, with a 140 mm (5.51 in) barrel.
Who makes the SIG MCX Rattler?
The SIG MCX Rattler is made by SIG Sauer (Germany).
When was the SIG MCX Rattler introduced?
The SIG MCX Rattler was introduced in 2018.
How does the SIG MCX Rattler operate?
The SIG MCX Rattler uses a gas operated short stroke piston 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
- United States Special Operations Command (USSOCOM)
- 2022
- Australian Army Special Forces
- 2024
- NSW Police Tactical Operations Unit
- Australia
- Jednostka Wojskowa GROM
- Poland
- JW Formoza
- Poland
- Spanish Navy
- Spain
- Guardia Civil
- Spain
Provenance
Confidence in this record
82%
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-mcx-rattler' \ --header 'X-API-Key: your_key'{ "id": "sig-mcx-rattler", "name": "SIG MCX Rattler", "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": "personal-defense-weapon", "name": "Personal Defense Weapon", "description": "Compact firearms designed for non-frontline military personnel" }, "country_of_origin": "US", "year_introduced": 2018, "barrel_length_mm": 140, "weight_empty_g": 2313, "action_type": "gas_operated_short_stroke_piston"}