---
title: "Compare two firearms head to head"
method: GET
path: "/v1/firearms/head-to-head"
tags: ["Firearm Discovery"]
---

# Compare two firearms head to head

`GET /v1/firearms/head-to-head`

## Request

- Base URL: `https://api.gunspec.io`
- URL: `https://api.gunspec.io/v1/firearms/head-to-head`
- Auth: one of:
  - API key in header `X-API-Key`
  - HTTP bearer

Returns a per-stat verdict between exactly two firearms, plus the win/loss/draw tally across all compared stats.

**Requires Builder tier or higher.**

## Query parameters

- `a` string, required
- `b` string, required

## Headers

- `If-None-Match` string

## Response `200`

Compare two firearms head to head

- object
  - `success` boolean, required: Always true on a successful response. Every error carries `false` and an `error` object instead.
  - `data` object, required: The response payload.
    - `a` HeadToHeadFirearm: One of the two compared firearms, as selected: the sixteen columns the verdicts are computed from, **snake_case**, under their database names.
      - `id` string, required: URL-safe slug identifying the firearm. Stable: it is what a mirror keys on.
      - `name` string, required: Display name, as the maker writes it.
      - `manufacturer_id` string, nullable: Slug of the manufacturer. `manufacturerId` on the camelCase endpoints.
      - `category_id` string, nullable: Slug of the category. `categoryId` on the camelCase endpoints.
      - `weight_empty_g` number, nullable: Unloaded weight in grams, without magazine.
      - `overall_length_mm` number, nullable: Overall length in millimetres.
      - `barrel_length_mm` number, nullable: Barrel length in millimetres, measured from the breech face.
      - `magazine_capacity` integer, nullable: Standard magazine capacity, in rounds.
      - `muzzle_velocity_mps` number, nullable: Muzzle velocity in metres per second, with the reference load.
      - `muzzle_energy_j` number, nullable: Muzzle energy in joules, with the reference load.
      - `effective_range_m` number, nullable: Effective range in metres.
      - `rate_of_fire_rpm` number, nullable: Cyclic rate of fire in rounds per minute; null for a semi-automatic or manual action.
      - `year_introduced` integer, nullable: Year the model was introduced.
      - `status` 'in_production' | 'discontinued' | 'out_of_production' | 'in_service' | 'limited_production' | 'prototype': Production status of a firearm. Closed: these are every value the catalog holds.
      - `country_of_origin` string, nullable: ISO 3166-1 alpha-2 code of the country of origin.
      - `action_type` string, nullable: Operating action as stored, underscored, e.g. `short_recoil`, `bolt_action`, `gas_operated`. The full vocabulary is `/v1/firearms/action-types`; a hyphenated value matches nothing.
    - `b` HeadToHeadFirearm: One of the two compared firearms, as selected: the sixteen columns the verdicts are computed from, **snake_case**, under their database names.
      - `id` string, required: URL-safe slug identifying the firearm. Stable: it is what a mirror keys on.
      - `name` string, required: Display name, as the maker writes it.
      - `manufacturer_id` string, nullable: Slug of the manufacturer. `manufacturerId` on the camelCase endpoints.
      - `category_id` string, nullable: Slug of the category. `categoryId` on the camelCase endpoints.
      - `weight_empty_g` number, nullable: Unloaded weight in grams, without magazine.
      - `overall_length_mm` number, nullable: Overall length in millimetres.
      - `barrel_length_mm` number, nullable: Barrel length in millimetres, measured from the breech face.
      - `magazine_capacity` integer, nullable: Standard magazine capacity, in rounds.
      - `muzzle_velocity_mps` number, nullable: Muzzle velocity in metres per second, with the reference load.
      - `muzzle_energy_j` number, nullable: Muzzle energy in joules, with the reference load.
      - `effective_range_m` number, nullable: Effective range in metres.
      - `rate_of_fire_rpm` number, nullable: Cyclic rate of fire in rounds per minute; null for a semi-automatic or manual action.
      - `year_introduced` integer, nullable: Year the model was introduced.
      - `status` 'in_production' | 'discontinued' | 'out_of_production' | 'in_service' | 'limited_production' | 'prototype': Production status of a firearm. Closed: these are every value the catalog holds.
      - `country_of_origin` string, nullable: ISO 3166-1 alpha-2 code of the country of origin.
      - `action_type` string, nullable: Operating action as stored, underscored, e.g. `short_recoil`, `bolt_action`, `gas_operated`. The full vocabulary is `/v1/firearms/action-types`; a hyphenated value matches nothing.
    - `verdicts` object: One verdict per compared stat, keyed by the stat's camelCase name (`weightEmptyG`, `overallLengthMm`, `barrelLengthMm`, `magazineCapacity`, `muzzleVelocityMps`, `muzzleEnergyJ`, `effectiveRangeM`, `rateOfFireRpm`). A stat neither firearm carries is omitted, so the key set is the stats that could be compared.

## Other responses

- `304`: Your copy is current. No body is sent, and this response does not count toward the daily request allowance.
- `400`: Validation error
- `401`: Missing or invalid API key
- `403`: The credential is valid and the caller is not permitted. Three causes, none of which reissuing a key changes: the plan is below the endpoint's tier, the account is suspended, or the key is not attached to the thing being acted on, meaning a user account for `/v1/me` or a shop for `/v1/vendor`. Distinct from 401, which means the credential is missing, malformed or expired and a new one can work.
- `404`: Resource not found
- `429`: A limit was reached. `RATE_LIMITED` is the per-minute limit: wait `Retry-After` seconds (a minute) and retry. `DAILY_CAP_EXCEEDED` is the plan's daily limit, per key: nothing will be served until the counters return to zero at midnight UTC. `MONTHLY_CAP_EXCEEDED` is the plan's monthly allowance, for the whole account: nothing will be served until midnight UTC on the first of next month, or until the plan changes. For both, `Retry-After` is the seconds until then and `error.resetsAt` says when as an instant. Calls made after a refusal are refused too and do not spend the month, and a free key that keeps calling is paused, so stop at the first one and resume at the reset.
- `500`: Internal server error

---

[API](https://skmtc.dev/gunspec/apis/gunspec-io-api.md) · [All operations](https://skmtc.dev/gunspec/apis/gunspec-io-api/llms.txt) · [OpenAPI document](https://skmtc.dev/gunspec/apis/gunspec-io-api/revisions/f2e974d8b05c?raw)