Consecutive Matching Striae (CMS)
Definition
A run of adjacent, individually corresponding striae observed across two bullets in the comparison microscope split field. The length of the longest CMS run is a principal identification criterion.
- Field
- Bullet striation comparison
- Instrument
- Comparison microscope, split field
- Metric
- Length of longest adjacent matching run
- Role
- Principal firearm identification criterion
Common questions
Why does the length of a consecutive matching run matter more than the total number of matching striae?+
Randomly toolmarked surfaces can occasionally produce a few matching striae by chance, but a long unbroken run of adjacent matches is statistically much less likely to occur coincidentally. Established CMS thresholds (developed through validation studies) are used to judge whether an observed run is long enough to support an identification conclusion.
What can interrupt an otherwise long consecutive matching striae run?+
Surface damage, corrosion, cleaning residue, or an intervening area of poor mark reproduction on either the questioned or known bullet can break a run into shorter segments, even where the same firearm produced both. Examiners account for this when assessing whether a broken run still supports identification.
Related terms
- AFTE Theory of Identification
- The Association of Firearm and Tool Mark Examiners' standard (1992, revised 2011) for reporting tool-mark comparison conclusions as Identification, Inconclusive, or Elimination...
- BalliScan 3D
- Foster and Freeman's three-dimensional topographic bullet comparison instrument that maps striated surfaces using structured-light interferometry for both optical and digital comparison workflows.
- Class Characteristics
- Features deliberately or systematically imparted to a group of items by design or manufacture, such as the calibre of a bullet, the...
- Comparison Microscope
- Two compound microscope bodies connected by an optical bridge that presents one half of each body's image in a single split eyepiece...
- Individual Characteristics
- Surface features on a fired bullet or cartridge case that arise from random or unique events (tool wear, corrosion, service damage) and...
- Leica FSC
- Leica Forensic Comparison System; a motorised zoom comparison microscope used in firearms and toolmark examination at CFSL laboratories in India, European national...
- PCAST Report (2016)
- The President's Council of Advisors on Science and Technology 2016 report on forensic science that found firearms mark analysis had not yet...
- Projectina PAG II
- A high-precision Swiss comparison microscope with motorised stages and quantitative striation-angle measurement, used at Swiss cantonal forensic labs and German LKA laboratories.
- Striations
- Fine parallel scratches on a fired bullet's surface, produced by asperities on the barrel's land surfaces. Each striation reflects the surface topography...