Metric Calibre Notation
Definition
Calibre designation using bullet diameter in millimetres multiplied by case length in millimetres (e.g. 9x19mm, 7.62x39mm, 5.56x45mm); standard in NATO and European commercial production.
- Format
- Bullet diameter x case length, mm
- Example
- 9x19mm, 7.62x39mm, 5.56x45mm
- Standard in
- NATO and European commercial production
Common questions
Why does metric notation include the case length while some other calibre systems do not?+
Including case length disambiguates cartridges that share the same bullet diameter but use different case lengths and pressures, such as distinguishing 7.62x39mm from 7.62x51mm, which is important for identifying the correct firearm and ammunition combination at a scene.
Can two cartridges with the same metric designation still differ in a way that matters forensically?+
Yes, bullet weight, propellant load, and headstamp can vary between manufacturers even for the same nominal metric designation, so the calibre notation narrows the field but headstamp and other markings are still needed to identify the specific manufacturer and lot.
Related terms
- CIP
- Commission Internationale Permanente pour l'Epreuve des Armes a Feu Portatives; the European proof body that standardises chamber and cartridge specifications for European...
- GRC Database
- General Rifling Characteristics database maintained by the FBI Laboratory's Firearms and Toolmarks Unit; includes an ammunition component section that references headstamp codes...
- Imperial Calibre Notation
- Calibre designation using decimal fractions of an inch, often with a name suffix indicating the designer or intended firearm (e.g. .45 ACP,...
- IOF
- Indian Ordnance Factory headstamp code (produced at Khadki / Kirkee, Pune); the primary Indian government producer of 9x19mm, .38 Special, and 7.62x51mm...
- LC
- Lake City Army Ammunition Plant headstamp code; the primary US military ammunition producer for small-arms calibres including 5.56x45mm, 7.62x51mm, and .50 BMG.
- NABIS
- National Ballistics Intelligence Service; the UK police intelligence service that maintains a national headstamp and firearm reference collection and coordinates ballistic intelligence...
- NATO Cross
- A circle with cross symbol stamped on military cartridge headstamps confirming the round meets the relevant NATO STANAG specification; found on production...
- Primer Sealant
- Coloured lacquer applied at the primer-to-case-head junction on military cartridges to prevent moisture ingress; colour varies by manufacturer and is not a...
- RG
- Radway Green headstamp code (UK); BAE Systems' Royal Ordnance Factories facility and primary UK military small-arms ammunition producer.
- S+B
- Sellier and Bellot headstamp code (Czech Republic, now part of CBC Group); a major European commercial and military-contract producer exported globally including...
- SAAMI
- Sporting Arms and Ammunition Manufacturers' Institute; the US voluntary standards body that publishes chamber and cartridge drawings and maximum average pressure (MAP)...