Forensic Examination of Firearms, Bullets, Shells and Cartridges
UGC-NET Paper 2 Unit V notes on firearm identification. Comparison microscopy, land and groove counts, breech-face and firing-pin marks, IBIS / NIBIN, AFTE scale.
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Firearm identification is the second bullet of UGC-NET Forensic Science Unit V, and it is the workhorse topic of the entire unit. The syllabus asks you to recall how a fired bullet or spent case is matched back to a single weapon, what marks the weapon leaves behind, and how the comparison microscope converts those marks into a court-admissible conclusion. NTA tests this bullet through MCQs on Goddard's comparison microscope (1925), land and groove counts on common service arms, the named mark families on a cartridge case, and the AFTE conclusion scale. Expect at least one question per cycle from this bullet.
Treat the topic as three parallel workflows. One workflow examines the bullet (rifling impressions, striations). One examines the spent case (firing pin, breech face, extractor, ejector, chamber marks). One handles shotgun pellets, wads and shot cups separately because smoothbore barrels do not impart rifling. Bind all three with the same instrument (the side-by-side comparison microscope) and the same end-point (an AFTE-scale conclusion that has to survive cross-examination under the Bharatiya Sakshya Adhiniyam 2023). The book chapters on firearm injuries and tool marks cover the wound and surface-mark sides of the same casework.
- Class characteristics
- Features common to a group of weapons of the same make and model. For bullets: caliber, number of lands and grooves, twist direction, groove width. Narrows the candidate weapons, never identifies one.
- Sub-class characteristics
- Features common to a small batch of weapons made with the same tool before the tool wore out. Sit between class and individual. Must be excluded before claiming identification.
- Individual characteristics
- Random microscopic imperfections in the rifling, breech face, firing pin or chamber that are unique to a single weapon and reproduce on every fired component. The basis of identification.
- Comparison microscope
- Two stages, two objectives, one optical bridge merging the two images into a single split eyepiece field. Invented by Calvin Goddard in 1925. Standard magnification 10x to 40x. Dual-stage rotation aligns striations.
- Rifling
- Helical lands (raised) and grooves (cut) inside a rifled barrel. Imparts spin to the bullet for gyroscopic stability. Notation like 5R or 6L means lands and grooves count + twist direction (Right or Left).
- Breech face
- The flat metal surface at the rear of the chamber that the case head slams against on firing. Machining striations on the breech face emboss onto the soft brass case head.
- AFTE conclusion scale
- Association of Firearm and Tool Mark Examiners scale: identification, inconclusive (subdivided A, B, C), elimination, unsuitable. The court-admissible vocabulary.
- IBIS / NIBIN
- Integrated Ballistic Identification System (Forensic Technology Inc., Canada) and Bureau of ATF's National Integrated Ballistic Information Network. Automated 3D imaging and correlation of bullet and case images across a database.
Comparison microscopy: the instrument that built forensic ballistics
Goddard, 1925, two stages and one bridge.
The single most testable historical fact in this bullet is that Calvin Goddard, working with Philip Gravelle, popularised the side-by-side comparison microscope in 1925 and used it to anchor the identification of the Sacco and Vanzetti bullets and (later) the St Valentine's Day Massacre casings. The instrument is two monocular microscopes mounted on a shared base, each with its own rotatable stage and objective, joined by an optical bridge that merges the two image halves into a single split field viewed through a binocular eyepiece. The examiner mounts the questioned bullet on one stage, the test-fired bullet on the other, rotates both stages until the lands and grooves align, and looks for striation matches across the seam.
Standard magnification for bullet comparison is 10x to 40x. Higher magnifications wash out the contrast on the brass jacket; lower magnifications miss fine striations. Modern instruments add coaxial fibre-optic illumination so the lighting on both halves is identical, because any difference in shadow direction kills the comparison. The dual-stage rotation is the single feature that distinguishes a comparison microscope from a pair of stereo microscopes side by side. The book chapter on tool mark evidence types and comparison uses the same instrument for chisel, screwdriver and bolt-cutter marks.
The conclusion at the eyepiece is binary in principle (does the striation pattern reproduce across the seam?) and probabilistic in practice (how many consecutive matching striae, on how many lands, with what known sub-class component?). The AFTE scale below converts that judgement into court vocabulary.
Bullet identification: class, sub-class and individual characteristics
Caliber narrows the field. Striations close it.
A fired bullet recovered from a body or a wall carries three layers of information that the examiner reads in sequence.
Class characteristics are set when the barrel is manufactured. The four NTA-testable ones are caliber (nominal bore diameter, for example .32 or 9 mm), the number of lands and grooves cut into the rifling, the direction of twist (Right or Left) and the width of the groove impressions on the bullet body. A bullet showing six grooves with a right twist (notation 6R) excludes every weapon with a different rifling specification. Class characteristics narrow the candidate population; they never identify a single weapon.
Indicative land and groove counts for common arms tested in MCQs:
| Weapon / cartridge | Caliber | Rifling notation | Comment |
|---|---|---|---|
| .32 S&W Long (Indian Ordnance revolver) | .32 in (7.65 mm) | 5R | Five lands, right twist. Standard Indian police service revolver |
| .38 Special | .38 in (9.07 mm) | 6R | Six lands, right twist. Common in older Indian and Western revolvers |
| .22 Long Rifle | .22 in (5.6 mm) |
Shell case examination: five named mark families
Firing pin, breech face, extractor, ejector, chamber. Memorise the locations.
A spent cartridge case carries more identifiable marks than a fired bullet, because the soft brass head is in metal-to-metal contact with five distinct surfaces of the weapon during the firing cycle. NTA tests the names and the anatomical location of each.
- Firing-pin impression is the dent in the centre of the primer cup left by the firing pin striking the primer. Its shape (hemispherical, elliptical, rectangular, drag-tail) is a class characteristic of the weapon design. Eccentricity (whether the dent sits dead-centre or off-centre on the primer) and tool-mark detail inside the impression are individual characteristics.
- Breech-face marks are the parallel or contoured striations transferred from the machining marks on the breech face onto the primer cup and (sometimes) the case head when chamber pressure slams the case rearward.
- Extractor marks are scrapes on the rim or extractor groove of the case made by the extractor hook as it pulls the case out of the chamber. Location: rim, 9 to 11 o'clock or 1 to 3 o'clock depending on weapon.
- Ejector marks are impact bruises on the case head where the ejector strikes the rim to throw the case clear of the action. Location: case head, opposite the extractor.
- Chamber marks are longitudinal scratches on the case body from the chamber walls, particularly on weapons with rough or fouled chambers. Useful when other marks are damaged.
Bolt-action and semi-auto weapons add magazine-lip marks on the case body (from chambering) and feed-ramp marks near the case mouth. These are less individualising but help confirm the action type.
The examiner photographs the case head with oblique low-angle lighting that throws each mark into shadow, then mounts the case on the comparison microscope stage alongside a test-fired case. Firing-pin and breech-face marks deliver most identifications; extractor and ejector marks are corroborative.
Shotgun examination: pellets, slugs, wads and shot cups
No rifling, so no striations. Different evidence, same logic.
Shotguns are smoothbore, so a fired pellet or slug does not carry rifling impressions and cannot be matched back to the barrel through striations. Shotgun examination relies on a different evidence set.
Pellet pattern at the recovered distance is matched to test-fired patterns from candidate shotguns at known distances and with known chokes (cylinder, improved cylinder, modified, full). A tighter pattern means a tighter choke or a shorter range; the candidate weapon must reproduce the questioned pattern within tolerance.
Wad and shot cup recovery is often the single best identifying evidence in a shotgun case. The plastic shot cup and over-powder wad are stamped by the manufacturer and carry the gauge, the make and frequently a batch code. Recovered wads also pick up striations from the bore and ring marks from the choke constriction.
Slug examination borrows the rifled-barrel toolkit if the slug was fired from a rifled slug barrel or rifled choke; otherwise the examiner relies on bore-diameter, mass and metallurgy class characteristics. The book chapter on firearm injuries (entry, exit, range) covers what the same pellets do to tissue.
AFTE conclusion scale and the IBIS / NIBIN-style databases
Identification, inconclusive (A, B, C), elimination, unsuitable.
The Association of Firearm and Tool Mark Examiners (AFTE) Theory of Identification gives the examiner a fixed vocabulary for the final report. NTA likes this list because each rung has a clean one-line definition.
- Identification. Sufficient agreement of individual characteristics so that the practical likelihood of another weapon producing them is excluded. This is the only conclusion that says "same weapon".
- Inconclusive A. Some agreement of individual characteristics and all class characteristics, but insufficient for identification.
- Inconclusive B. Agreement of all class characteristics, no disagreement of individual characteristics.
- Inconclusive C. Agreement of all class characteristics, with some disagreement of individual characteristics.
- Elimination. Significant disagreement of class or individual characteristics. Different weapon.
- Unsuitable. Item lacks sufficient detail to support any comparison.
Modern ballistics labs front the manual comparison with an automated 3D imaging and correlation database. The two NTA-testable names are IBIS (Integrated Ballistic Identification System, Forensic Technology Inc., Canada) and NIBIN (National Integrated Ballistic Information Network, run by US ATF). Both image the breech face and firing-pin region of a case and the bullet body in 3D, generate a numerical correlation score against the database, and produce a ranked candidate list that an examiner then confirms on the comparison microscope. India runs ballistics divisions at CFSL Chandigarh and CFSL Hyderabad under the Directorate of Forensic Science Services (DFSS), and the National Ballistic Data Centre concept under the Bureau of Police Research and Development (BPRD) has been piloted as the Indian equivalent of NIBIN. State SFSLs maintain their own test-fired reference collections for licensed weapons.
The expert report ends in court. Under the Bharatiya Sakshya Adhiniyam 2023,