Browning M3M
- Category
- Machine Gun
- Barrel
- 914 mm
- Weight, empty
- 35.80 kg
- Introduced
- 2004
About
What it is, and why it matters
The Browning M3M is a .50 BMG (12.7x99mm NATO) belt-fed heavy machine gun developed by FN Herstal as an evolution of the M3 aircraft variant of the legendary Browning M2. Designed primarily for rotary-wing aircraft as a door- or pintle-mounted defensive weapon, it uses a short-recoil, open-bolt action and a dual recoil buffer system to deliver a high cyclic rate of fire of up to 1,100 rounds per minute while reducing felt recoil and barrel wear. Adopted by the U.S. Navy and Marine Corps in 2004 under the designation GAU-21, it equips platforms such as the H-60, CH-53, UH-1, and MV-22, providing suppressive fire out to roughly 1,850 meters.
The M3M traces its lineage directly to John Moses Browning's M2 of the 1920s; FN Herstal modernized the aircraft-rate M3 variant into a rotary-wing defensive weapon, which the U.S. Navy adopted in 2004 as the GAU-21.
Designated GAU-21 by the U.S. military when fitted to aircraft soft mounts. Features a quick-change barrel and disintegrating-link belt feed compatible with 100-, 300-, and 600-round ammunition containers.
Specification
Everything measured
IdentityWhat it is, who built it and when.
- Manufacturer
- FN Herstal
- Category
- Machine Gun
- Country
- Belgium
- Status
- In production
- Produced
- 2004
DimensionsAs issued, without a magazine or an optic.
- Barrel
- 914 mm
- Overall length
- 1520 mm
- Weight, empty
- 35.80 kg
ActionHow it cycles, what trips it, and what feeds it.
- Action
- Short recoil
- Firing mechanism
- Open bolt
- Capacity
- 600
- Magazine
- Belt
MaterialsEach swatch is the material itself, not a colour chosen to stand for it.
- Frame
- Steel
- Barrel
- Steel
- Finish
- Phosphate
BallisticsFrom the service cartridge, not a handload.
- Muzzle velocity
- 880 m/s
- Muzzle energy
- 17010 J
- Effective range
- 1850 m
- Maximum range
- 6500 m
- Rate of fire
- 1100 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.
Open bolt operation
Dual recoil buffer
Quick change barrel
Soft mount compatible
Disintegrating link belt 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 261 machine guns | 35.80 kg | 10.50 kg | Heavier than about 90% |
| Overall lengthAmong 260 machine guns | 1520 mm | 1156 mm | Longer than about 90% |
| Barrel lengthAmong 257 machine guns | 914 mm | 605 mm | Longer than about 90% |
| Magazine capacityAmong 222 machine guns | 600 | 50 | Holds more rounds than about 90% |
Its place in the rankings
Answers
Questions about the Browning M3M
How much does the Browning M3M weigh?
The Browning M3M weighs 35.80 kg (78.93 lb) empty.
What caliber is the Browning M3M?
The Browning M3M is chambered in .50 BMG.
How many rounds does the Browning M3M hold?
The Browning M3M holds 600 rounds, fed from a belt.
How long is the Browning M3M?
The Browning M3M is 1520 mm (59.8 in) long overall, with a 914 mm (36.0 in) barrel.
Who makes the Browning M3M?
The Browning M3M is made by FN Herstal (Belgium). It was designed by FN Herstal.
When was the Browning M3M introduced?
The Browning M3M was introduced in 2004.
How does the Browning M3M operate?
The Browning M3M uses a short recoil 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
- United States Navy
- 2004
- United States Marine Corps
- 2004
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/browning-m3m' \ --header 'X-API-Key: your_key'{ "id": "browning-m3m", "name": "Browning M3M", "manufacturer": { "id": "fn-herstal", "name": "FN Herstal", "countryCode": "BE", "foundedYear": 1889, "website": "https://www.fnherstal.com", "logoUrl": null, "description": null, "status": null, "defunctYear": null, "stateOwned": null, "makesFirearms": null, "parentId": null, "predecessorId": null, "createdAt": "2026-02-11 23:44:38", "updatedAt": "2026-02-18 03:43:43", "version": "868b12ac455d24b965edddf486bafb1892f606961311b1ab9907556e3a23b075" }, "category": { "id": "machine-gun", "name": "Machine Gun", "description": "Fully automatic firearms for sustained fire" }, "country_of_origin": "BE", "year_introduced": 2004, "barrel_length_mm": 914, "weight_empty_g": 35800, "action_type": "short_recoil"}