FN 509 Midsize
- Category
- Pistol
- Barrel
- 102 mm
- Weight, empty
- 751 g
- Introduced
- 2020
About
What it is, and why it matters
The FN 509 Midsize is a striker-fired, short-recoil-operated semi-automatic pistol chambered in 9x19mm Parabellum. It pairs a compact-length 4.0-inch cold hammer-forged stainless steel barrel and 15-round magazine with the full-size grip ergonomics of the FN 509 family, splitting the difference between the standard 509 and the subcompact 509 Compact. It features fully ambidextrous controls, interchangeable backstraps, a polymer frame with replaceable steel rails, and no manual safety.
The 509 line grew out of FN's entry in the U.S. Army's Modular Handgun System trial; the Midsize carries the winning ergonomics into a carry-friendly barrel-and-slide length while keeping the full-size 15-round grip.
Positioned between the full-size FN 509 and the FN 509 Compact; accepts full-size 509 magazines. Also offered with a factory optics-ready slide cut (509 Midsize MRD).
Specification
Everything measured
IdentityWhat it is, who built it and when.
- Manufacturer
- FN Herstal
- Category
- Pistol
- Country
- United States
- Status
- In production
- Produced
- 2020
- Variant of
- Midsize
DimensionsAs issued, without a magazine or an optic.
- Barrel
- 102 mm
- Overall length
- 188 mm
- Height
- 132 mm
- Width
- 34 mm
- Sight radius
- 147 mm
- Weight, empty
- 751 g
ActionHow it cycles, what trips it, and what feeds it.
- Action
- Short recoil
- Firing mechanism
- Striker fired
- Trigger
- Single stage
- Trigger pull
- 29.0 N
- Capacity
- 15
- Magazine
- Detachable box
MaterialsEach swatch is the material itself, not a colour chosen to stand for it.
- Frame
- Polymer
- Slide
- Stainless steel
- Barrel
- Stainless steel
- Finish
- Black
BallisticsFrom the service cartridge, not a handload.
- Muzzle velocity
- 360 m/s
- Muzzle energy
- 481 J
- Effective range
- 50 m
- Maximum range
- 1800 m
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.
Fully ambidextrous controls
Reversible magazine release
Interchangeable backstraps
Accessory rail
Cold hammer forged barrel
Loaded chamber indicator
Flat faced trigger
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 560 9x19mm Parabellum pistols | 751 g | 765 g | Near the median |
| Overall lengthAmong 559 9x19mm Parabellum pistols | 188 mm | 191 mm | Shorter than about 60% |
| Barrel lengthAmong 569 9x19mm Parabellum pistols | 102 mm | 105 mm | Shorter than about 60% |
| Magazine capacityAmong 571 9x19mm Parabellum pistols | 15 | 15 | Near the median |
Answers
Questions about the FN 509 Midsize
How much does the FN 509 Midsize weigh?
The FN 509 Midsize weighs 751 g (1.66 lb) empty.
What caliber is the FN 509 Midsize?
The FN 509 Midsize is chambered in 9x19mm Parabellum.
How many rounds does the FN 509 Midsize hold?
The FN 509 Midsize holds 15 rounds, fed from a detachable box magazine.
How long is the FN 509 Midsize?
The FN 509 Midsize is 188 mm (7.40 in) long overall, with a 102 mm (4.02 in) barrel.
Who makes the FN 509 Midsize?
The FN 509 Midsize is made by FN Herstal (Belgium).
When was the FN 509 Midsize introduced?
The FN 509 Midsize was introduced in 2020.
How does the FN 509 Midsize operate?
The FN 509 Midsize uses a short recoil action, and its firing mechanism is striker 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.
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/fn-509-midsize' \ --header 'X-API-Key: your_key'{ "id": "fn-509-midsize", "name": "FN 509 Midsize", "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": "pistol", "name": "Pistol", "description": "Handguns designed to be fired with one or two hands" }, "country_of_origin": "US", "year_introduced": 2020, "barrel_length_mm": 102, "weight_empty_g": 751, "action_type": "short_recoil"}