SIG Sauer MPX K
- Category
- Personal Defense Weapon
- Barrel
- 114 mm
- Weight, empty
- 2.27 kg
- Introduced
- 2015
About
What it is, and why it matters
The SIG Sauer MPX K is the compact 'Kurz' configuration of the MPX, built around a 4.5-inch cold-hammer-forged barrel with a short M-LOK handguard. It retains the MPX's short-stroke gas-piston operating system firing from a closed rotating bolt, AR-pattern lower-receiver ergonomics, and proprietary translucent polymer magazines (typically 35 rounds). With a 1:10 twist barrel and a free-floated, suppressor-ready muzzle, the MPX K is positioned as a controllable, suppressed-capable close-quarters 9mm carbine/PDW. Commercial versions are semi-automatic-only braced pistols or short-barreled rifles; the select-fire submachine-gun version is offered to military and law-enforcement users.
Reviewers nicknamed the MPX K the 'MP5 killer' - SIG's bet that a gas-piston 9mm could out-shoot the half-century-old roller-delayed icon at its own compact-PDW game, trading the MP5's legendary smoothness for AR-15 ergonomics and a quick-change barrel.
The MPX K was frequently positioned by reviewers as a modern competitor to the Heckler & Koch MP5K. Its gas-piston system and internal buffer give it markedly flatter recoil than blowback PDWs of similar size. Magazines are proprietary and not interchangeable with Glock, Colt SMG, or MP5 feed devices. Rate-of-fire figure applies to the select-fire SMG variant; commercial models are semi-automatic only.
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
- 2015
- Variant of
- Compact
DimensionsAs issued, without a magazine or an optic.
- Barrel
- 114 mm
- Overall length
- 565 mm
- Height
- 203 mm
- Width
- 61 mm
- Weight, empty
- 2.27 kg
ActionHow it cycles, what trips it, and what feeds it.
- Action
- Gas operated short stroke
- Firing mechanism
- Hammer fired
- Trigger
- Single stage
- Capacity
- 35
- Magazine
- Detachable box
MaterialsEach swatch is the material itself, not a colour chosen to stand for it.
- Frame
- Aluminum
- Barrel
- Steel
- Stock
- Polymer
- Finish
- Nitride
BallisticsFrom the service cartridge, not a handload.
- Muzzle velocity
- 390 m/s
- Muzzle energy
- 567 J
- Effective range
- 100 m
- Maximum range
- 200 m
- Rate of fire
- 850 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
Closed bolt firing
Ambidextrous controls
M-lok handguard
Free floating barrel- Handstop
Ar15 style controls
Picatinny rail
Translucent polymer magazine
Suppressor ready
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 | 2.27 kg | 2.23 kg | Near the median |
| Overall lengthAmong 53 personal defense weapons | 565 mm | 582 mm | Near the median |
| Barrel lengthAmong 55 personal defense weapons | 114 mm | 168 mm | Shorter than about 90% |
| Magazine capacityAmong 25 9x19mm Parabellum personal defense weapons | 35 | 20 | Holds more rounds than about 90% |
Answers
Questions about the SIG Sauer MPX K
How much does the SIG Sauer MPX K weigh?
The SIG Sauer MPX K weighs 2.27 kg (5.00 lb) empty.
What caliber is the SIG Sauer MPX K?
The SIG Sauer MPX K is chambered in 9x19mm Parabellum.
How many rounds does the SIG Sauer MPX K hold?
The SIG Sauer MPX K holds 35 rounds, fed from a detachable box magazine.
How long is the SIG Sauer MPX K?
The SIG Sauer MPX K is 565 mm (22.2 in) long overall, with a 114 mm (4.49 in) barrel.
Who makes the SIG Sauer MPX K?
The SIG Sauer MPX K is made by SIG Sauer (Germany). It was designed by SIG Sauer engineering team.
When was the SIG Sauer MPX K introduced?
The SIG Sauer MPX K was introduced in 2015.
How does the SIG Sauer MPX K operate?
The SIG Sauer MPX K uses a gas operated short stroke 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
- US Law Enforcement (Various)
- United States
Provenance
Confidence in this record
70%
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-mpx-k' \ --header 'X-API-Key: your_key'{ "id": "sig-mpx-k", "name": "SIG Sauer MPX K", "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": 2015, "barrel_length_mm": 114, "weight_empty_g": 2268, "action_type": "gas_operated_short_stroke"}