Grooves
Definition
The recessed channels cut into a rifled barrel between the lands. They create raised land impressions on a fired bullet's surface.
- Location
- Recessed channels in a rifled barrel
- Position relative to lands
- Cut between the raised lands
- Effect on bullet
- Leaves raised groove impressions on the bullet
- Measured properties
- Width, depth, number, twist direction
Common questions
Why do grooves produce raised marks on a bullet rather than grooved marks?+
The bullet is slightly larger than the bore, so as it is forced through the barrel the lands bite into and compress the bullet's surface, leaving depressed land impressions, while bullet metal is forced outward into the recessed grooves, leaving raised groove impressions at those points.
How do groove measurements help narrow down a firearm's make and model?+
The number of grooves, their width, and the direction and rate of twist together form a class characteristic pattern that examiners compare against reference databases of known rifling specifications, narrowing the pool of firearm models capable of having fired a recovered bullet before individual toolmark comparison begins.
Related terms
- BKA
- Bundeskriminalamt, the German Federal Criminal Police Office, which operates the German GRC and ballistic identification database feeding the European EBIS network.
- CFSL
- Central Forensic Science Laboratory: a central government lab operating under DFSS. India has CFSLs at New Delhi, Hyderabad, Chandigarh, Kolkata, Pune, Guwahati,...
- General Rifling Characteristics (GRC)
- The class-level barrel properties (land count, groove count, land width, groove width, twist direction, twist rate) that allow a fired bullet to...
- Lands
- The raised ridges of a rifled barrel. Lands engrave groove impressions into the surface of a passing bullet. They are the harder...
- Left-Hand Twist (LHT)
- Rifling that spirals counterclockwise toward the muzzle. The defining house convention of Colt Manufacturing Company and of the Lee-Enfield rifle family.
- NABIS
- National Ballistics Intelligence Service; the UK police intelligence service that maintains a national headstamp and firearm reference collection and coordinates ballistic intelligence...
- Polygonal Rifling
- A rifling form that uses a rounded hexagonal or octagonal bore profile instead of discrete lands and grooves. Characteristic of Glock barrels;...
- Rate of Twist
- The barrel length required for the rifling to complete one full helical revolution, expressed as a ratio (e.g. 1:9 means one complete...
- Right-Hand Twist (RHT)
- Rifling that spirals clockwise toward the muzzle when viewed from the breech. Used by the majority of the world's firearm manufacturers.