Maximum Average Pressure (MAP)
Definition
The SAAMI statistical ceiling for mean chamber pressure across a production lot of cartridges, at specified temperature and barrel conditions. CIP uses maximum mean pressure (MMP) expressed in MPa. Forensic overpressure determinations compare reconstruction estimates against these figures.
- Standard body
- SAAMI (US)
- Equivalent CIP term
- Maximum mean pressure (MMP), in MPa
- What it caps
- Mean chamber pressure across a production lot
- Forensic use
- Benchmark for overpressure reconstruction
Common questions
Why compare a reconstruction estimate against MAP rather than a single fired round's pressure?+
MAP is a statistical lot ceiling, not a per-round measurement, so it gives investigators a defensible upper bound for normal ammunition performance against which an unusually high pressure estimate can be flagged as anomalous.
Does exceeding MAP always mean the ammunition or firearm failed?+
Not necessarily; individual rounds within a lot vary, and exceeding MAP on one round is expected statistically, so overpressure conclusions require broader evidence such as case deformation, barrel damage, or repeated anomalies, not a single reading alone.
Related terms
- Chamber Pressure
- The gas pressure inside the firearm's chamber and bore during combustion of the propellant charge. Measured by piezoelectric transducer in psi (SAAMI)...
- Hangfire
- A delay between firing-pin strike and cartridge ignition, ranging from fractions of a second to several seconds. Caused by degraded or moisture-contaminated...
- Piezoelectric Transducer
- A quartz or ceramic crystal sensor mounted in a barrel port that converts chamber pressure to a measurable electrical charge. The basis...
- Slamfire
- Unintended cartridge ignition during bolt closure, without a discrete trigger pull. Caused by free-floating firing pin inertia or primer over-sensitivity. Produces automatic-like...
- Squib Load
- An underpowered cartridge where the propellant fails to generate enough gas to fully propel the bullet out of the barrel. The bullet...
- Throat Erosion
- Wear of the bore at the point where the rifling begins (the throat or leade), caused by hot propellant gas and bullet...