Heckler & Koch HK21
- Category
- Machine Gun
- Barrel
- 450 mm
- Weight, empty
- 7.30 kg
- Introduced
- 1961
About
What it is, and why it matters
The Heckler & Koch HK21 is a German general-purpose machine gun introduced in 1961 and derived from the G3 battle rifle, sharing its roller-delayed blowback action and many components. Chambered in 7.62x51mm NATO, it fires from a closed bolt at roughly 900 rounds per minute and feeds from disintegrating or non-disintegrating belts, with conversion kits allowing magazine feed. Its quick-change barrel and interchangeable feed modules made it a flexible squad and sustained-fire weapon, and it was widely exported and license-produced in Portugal (m/968) and Mexico (MG21).
Because it is essentially a belt-fed G3, an HK21 gunner can field-strip and understand the action of his squad's rifles and machine gun interchangeably - the roller-delayed bolt is the same family throughout, a deliberate H&K logistics philosophy.
Belt feed is the standard configuration; a feed-module swap converts the gun to box-magazine feed. The closely related HK11 is the magazine-fed automatic-rifle counterpart. In the 1980s the design was modernized into the modular 'E' family (HK11E/HK13E/HK21E).
Specification
Everything measured
IdentityWhat it is, who built it and when.
- Manufacturer
- Heckler & Koch
- Category
- Machine Gun
- Country
- Germany
- Status
- In service
- Produced
- 1961
DimensionsAs issued, without a magazine or an optic.
- Barrel
- 450 mm
- Overall length
- 1020 mm
- Weight, empty
- 7.30 kg
ActionHow it cycles, what trips it, and what feeds it.
- Action
- Roller delayed blowback
- Firing mechanism
- Hammer fired
- 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
- 823 m/s
- Muzzle energy
- 3226 J
- Effective range
- 1200 m
- Maximum range
- 3500 m
- Rate of fire
- 900 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
Closed bolt operation- Interchangeable feed unit
Bipod- Tripod mountable
Convertible belt or magazine feed
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 | 7.30 kg | 10.51 kg | Lighter than about 90% |
| Overall lengthAmong 32 7.62x51mm NATO machine guns | 1020 mm | 1149 mm | Shorter than about 80% |
| Barrel lengthAmong 32 7.62x51mm NATO machine guns | 450 mm | 559 mm | Shorter than about 90% |
Its place in the rankings
Answers
Questions about the Heckler & Koch HK21
How much does the Heckler & Koch HK21 weigh?
The Heckler & Koch HK21 weighs 7.30 kg (16.09 lb) empty. It is the 3rd lightest of 32 7.62x51mm NATO machine guns in the catalogue.
What caliber is the Heckler & Koch HK21?
The Heckler & Koch HK21 is chambered in 7.62x51mm NATO.
How long is the Heckler & Koch HK21?
The Heckler & Koch HK21 is 1020 mm (40.2 in) long overall, with a 450 mm (17.7 in) barrel.
Who makes the Heckler & Koch HK21?
The Heckler & Koch HK21 is made by Heckler & Koch (Germany).
When was the Heckler & Koch HK21 introduced?
The Heckler & Koch HK21 was introduced in 1961.
How does the Heckler & Koch HK21 operate?
The Heckler & Koch HK21 uses a roller delayed blowback 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
- Bundeswehr
- Germany
- Portuguese Armed Forces
- Portugal
- Mexican Armed Forces
- Mexico
- Royal Thai Armed Forces
- Thailand
- United States special operations forces
- United States
Provenance
Confidence in this record
78%
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/hk21' \ --header 'X-API-Key: your_key'{ "id": "hk21", "name": "Heckler & Koch HK21", "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": 1961, "barrel_length_mm": 450, "weight_empty_g": 7300, "action_type": "roller_delayed_blowback"}