HK121
- Category
- Machine Gun
- Barrel
- 550 mm
- Weight, empty
- 10.80 kg
- Introduced
- 2011
About
What it is, and why it matters
The HK121 is a gas-operated, belt-fed general-purpose machine gun developed by Heckler & Koch and chambered in 7.62x51mm NATO. Introduced in 2011, it uses a rotating-bolt, open-bolt action firing from a disintegrating belt, with a quick-change barrel, adjustable gas regulator, folding bipod, and collapsible stock. Adopted by the German Army as the MG5 to succeed the Cold War-era MG3, it can be deployed in light infantry, coaxial, and vehicle-mounted roles with an effective range of roughly 1,000 meters.
Developed as the modern successor to the legendary MG3 (itself descended from the WWII-era MG42), the HK121 was Heckler & Koch's answer to NATO's need for a lighter, more controllable 7.62mm general-purpose machine gun. After extensive trials it was adopted by the Bundeswehr under the designation MG5.
Fires fully automatic only, fed by 50- or 120-round disintegrating DM60/M13-type belts. The selectable gas regulator allows the cyclic rate to be set between roughly 640 and 800 rounds per minute. Issued in multiple barrel-length variants (MG5, MG5A1, MG5A2, MG5S) for different mission profiles.
Specification
Everything measured
IdentityWhat it is, who built it and when.
- Manufacturer
- Heckler & Koch
- Category
- Machine Gun
- Country
- Germany
- Status
- In production
- Produced
- 2011
DimensionsAs issued, without a magazine or an optic.
- Barrel
- 550 mm
- Overall length
- 1165 mm
- Weight, empty
- 10.80 kg
ActionHow it cycles, what trips it, and what feeds it.
- Action
- Gas operated
- Firing mechanism
- Open bolt
- Trigger
- Single stage
- Magazine
- Belt
MaterialsEach swatch is the material itself, not a colour chosen to stand for it.
- Frame
- Steel
- Barrel
- Steel
- Stock
- Polymer
- Finish
- Phosphate
BallisticsFrom the service cartridge, not a handload.
- Muzzle velocity
- 810 m/s
- Muzzle energy
- 3116 J
- Effective range
- 1000 m
- Maximum range
- 3500 m
- Rate of fire
- 700 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.
Quick change barrel
Adjustable gas regulator
Rotating bolt
Picatinny rail
Folding bipod
Collapsible stock
Ambidextrous controls
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 32 7.62x51mm NATO machine guns | 10.80 kg | 10.51 kg | Heavier than about 60% |
| Overall lengthAmong 32 7.62x51mm NATO machine guns | 1165 mm | 1149 mm | Longer than about 60% |
| Barrel lengthAmong 32 7.62x51mm NATO machine guns | 550 mm | 559 mm | Shorter than about 60% |
Answers
Questions about the HK121
How much does the HK121 weigh?
The HK121 weighs 10.80 kg (23.81 lb) empty.
What caliber is the HK121?
The HK121 is chambered in 7.62x51mm NATO.
How long is the HK121?
The HK121 is 1165 mm (45.9 in) long overall, with a 550 mm (21.7 in) barrel.
Who makes the HK121?
The HK121 is made by Heckler & Koch (Germany). It was designed by Heckler & Koch.
When was the HK121 introduced?
The HK121 was introduced in 2011.
How does the HK121 operate?
The HK121 uses a gas operated action, and its firing mechanism is open bolt.
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
- German Army
- 2015
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/hk121' \ --header 'X-API-Key: your_key'{ "id": "hk121", "name": "HK121", "manufacturer": { "id": "heckler-koch", "name": "Heckler & Koch", "countryCode": "DE", "foundedYear": 1949, "website": "https://www.heckler-koch.com", "logoUrl": null, "description": null, "status": null, "defunctYear": null, "stateOwned": null, "makesFirearms": null, "parentId": null, "predecessorId": null, "createdAt": "2026-04-05 22:24:37", "updatedAt": "2026-04-05 22:24:37", "version": "ae60994f5b45d604da21fcd14b728cfa9d2e62000c92e596de4c48c4be768979" }, "category": { "id": "machine-gun", "name": "Machine Gun", "description": "Fully automatic firearms for sustained fire" }, "country_of_origin": "DE", "year_introduced": 2011, "barrel_length_mm": 550, "weight_empty_g": 10800, "action_type": "gas_operated"}