GunSpec

Calibers

Browse ammunition calibers with ballistic data, dimensions, and linked firearms. Useful for filtering, cross-referencing, and ammunition compatibility checks.

Auth RequiredBuilder+

Caliber Family Tree

Returns the cartridge together with its parent and every cartridge derived from it.

GET/v1/calibers/{id}/family

Builder+

  • stringheaderrequired

    Your API key. Authorization: Bearer <key> is accepted in its place.

  • stringrequired

    Caliber slug

    Accepts
    a lowercase slug: letters, digits and hyphens
    Example

The example asks for 9x19mm-parabellum. See that record on gunspec.io, rendered for people.

application/json

  • object

    The response payload.

  • Caliber[]

    The parent chain, nearest first, up to 20 deep.

  • string

    URL-safe slug identifying the cartridge, e.g. 9x19mm-parabellum.

  • string

    Display name, as the maker writes it.

  • string[]

    Other names this cartridge is sold or written as.

  • string | null

    NATO designation where the cartridge has one, e.g. 9mm NATO. Null otherwise.

  • number | null

    Bullet diameter in millimetres.

  • number | null

    Case neck outside diameter in millimetres.

  • number | null

    Bottleneck cases only.

  • number | null

    Case base diameter in millimetres, ahead of the extractor groove.

  • number | null

    Rim diameter in millimetres.

  • number | null

    Rim thickness in millimetres.

  • number | null

    Case length in millimetres.

  • number | null

    Overall length in millimetres, stock extended where it folds or collapses.

  • Caliber

    The requested caliber

  • string

    URL-safe slug identifying the cartridge, e.g. 9x19mm-parabellum.

  • string

    Display name, as the maker writes it.

  • string[]

    Other names this cartridge is sold or written as.

  • string | null

    NATO designation where the cartridge has one, e.g. 9mm NATO. Null otherwise.

  • number | null

    Bullet diameter in millimetres.

  • number | null

    Case neck outside diameter in millimetres.

  • number | null

    Bottleneck cases only.

  • number | null

    Case base diameter in millimetres, ahead of the extractor groove.

  • number | null

    Rim diameter in millimetres.

  • number | null

    Rim thickness in millimetres.

  • number | null

    Case length in millimetres.

  • number | null

    Overall length in millimetres, stock extended where it folds or collapses.

  • Caliber[]

    Every cartridge derived from this one, up to 50 rows.

  • string

    URL-safe slug identifying the cartridge, e.g. 9x19mm-parabellum.

  • string

    Display name, as the maker writes it.

  • string[]

    Other names this cartridge is sold or written as.

  • string | null

    NATO designation where the cartridge has one, e.g. 9mm NATO. Null otherwise.

  • number | null

    Bullet diameter in millimetres.

  • number | null

    Case neck outside diameter in millimetres.

  • number | null

    Bottleneck cases only.

  • number | null

    Case base diameter in millimetres, ahead of the extractor groove.

  • number | null

    Rim diameter in millimetres.

  • number | null

    Rim thickness in millimetres.

  • number | null

    Case length in millimetres.

  • number | null

    Overall length in millimetres, stock extended where it folds or collapses.

  • 400VALIDATION_ERRORValidation error
  • 401UNAUTHORIZEDAPI key required
  • 403FORBIDDENValid key, not permitted
  • 404NOT_FOUNDResource not found
  • 429RATE_LIMITEDRate limit exceeded
  • 500INTERNAL_ERRORUnexpected server error

Requires Builder tier or higher.

Ancestors are returned root-first (oldest ancestor at index 0).

Descendants include all calibers that trace their lineage back to this caliber.

Unlike the parent-chain endpoint, this returns the full bidirectional tree.

Full rate limits

Minimum tier
Builder+
Monthly quota
25,000/mo
Rate limit
60/min
Daily cap
5,000

Figures shown are for this endpoint's minimum tier. Higher tiers raise every limit.