Handguns: Revolvers and Semi-Automatic Pistols

The revolver's defining feature is its rotating cylinder, which holds between five and eight cartridges depending on calibre and design. Each chamber in the cylinder lines up with the barrel in sequence as the action cycles. Unlike a semi-automatic, no case is ejected during firing; spent cases remain in their chambers until the shooter manually removes them, either by opening the swing-out cylinder and using the ejector rod (on double-action revolvers) or by removing each case individually from a fixed cylinder (on the earliest single-action designs).

A single-action revolver requires the hammer to be manually cocked for each shot. The Colt Single Action Army (Model P, 1873) introduced this format to mass production; it has six chambers, a fixed cylinder released by a loading gate, and a transfer bar absent in original designs (making original SAA variants subject to accidental discharge if dropped with all six chambers loaded). The firing-pin impression on a SAA case is round, centrally placed, and deeply struck by the fixed hammer-mounted firing pin. Forensic examiners encountering original Colt SAA or its copies (the Italian Uberti, the Spanish Llama) look for this round, hard primer crater as a class characteristic.

A double-action revolver can be fired either by cocking the hammer manually first (single-action mode, lighter trigger pull, more precise) or by a long, continuous trigger pull that both cocks and releases the hammer in one motion (double-action mode, heavier pull, faster). Smith and Wesson standardised the double-action swing-out cylinder revolver with the Hand Ejector series (1896 onward). The S+W Model 10 in .38 Special became the standard US police sidearm from the 1950s through the 1980s, equipped to virtually every American municipal police department and to the Metropolitan Police in London until the shift to Glock 17 and Glock 19 in the 1990s. In India, the .38 S+W Model 10 was issued to senior Indian Police Service officers and remains in limited service in some state forces.

Contemporary double-action revolvers include the S+W Model 686 (stainless, .357 Magnum, six or seven chambers), the S+W Model 442 Airweight (.38 Special, five-shot J-frame), and the Ruger GP100 (.357 Magnum). In Germany, the Arminius HW-38 has been produced since the 1960s and appears in German casework. In France, the MANURHIN MR 73 .357 Magnum remained in French Gendarmerie service for decades. All double-action revolvers share the class characteristic of a spring-driven firing pin that strikes primers with a lighter blow than single-action designs, producing a slightly shallower firing-pin impression whose exact geometry varies by brand and model.

The revolver's limitation in forensic individualisation centres on the breech face. Because the cylinder sits behind the barrel and rotates between shots, the fired case's base contacts the recoil shield (the fixed plate at the rear of the frame) rather than a machined bolt face. The rifling characteristics on the projectile remain the primary individual-identification link between the fired bullet and the specific barrel. The recoil-shield contact and the firing-pin bushing around the firing-pin aperture leave specific marks. Cylinder-to-barrel misalignment, either from wear or a poorly timed action, leaves a distinctive gas-erosion ring at the case mouth where propellant gas leaks past the cylinder gap.

The semi-automatic pistol fires one round per trigger pull, automatically chambers the next round from the magazine using energy recovered from the fired round, and ejects the spent case through an ejection port. The magazine, inserted in the grip, stores multiple rounds. When the last round is fired, the slide locks back, visually and tactilely indicating an empty weapon.

The tilting-barrel short-recoil system developed by John Moses Browning, embodied in the Colt M1911 (patented 1905, adopted by the US military in 1911) and the Browning Hi-Power (FN Grande Puissance, 1935, adopted by Belgium and numerous other military forces), remains the dominant operating principle in service pistols. In this system, the barrel and slide are locked together at the moment of firing. Recoil drives both rearward, but after a short distance (the short-recoil distance), the barrel's rear tilts down and unlocks from the slide. The slide continues rearward alone, extracting and ejecting the spent case. A recoil spring returns the slide forward, stripping a fresh round from the magazine and chambering it, and the barrel cams back up to lock with the slide.

The ejected case in a short-recoil pistol carries: the firing-pin impression (round in most modern pistols, rectangular in some older German designs), the breech-face marks from the machined bolt face of the slide, an extractor mark on the case rim where the spring-loaded extractor grabs the rim after extraction, and an ejector mark on the case head where the ejector strikes the case to flip it out of the ejection port. These four marks, compared on the comparison microscope against test-fires from a suspect weapon, constitute the primary individualising features in cartridge-case comparison.

Glock Ges.m.b.H. (Deutsch-Wagram, Austria) introduced a polymer frame and striker-fire ignition to mass production with the Glock 17 in 1982, which was adopted by the Austrian Bundesheer in 1982 as the Pistole 80. A striker-fire mechanism replaces the external hammer with a captive firing pin (striker) that is partially pre-cocked by the slide cycle and fully cocked by the final millimetres of trigger travel. There is no external hammer, no hammer fall, and no decocker. The Glock firing-pin impression is a round punch mark within a larger, circular firing-pin safety impression. The Glock 17 (9x19mm, 17-round magazine) and Glock 19 (9x19mm, compact, 15-round magazine) are among the most widely distributed police and civilian pistols globally. The Metropolitan Police Service adopted the Glock 17 as its principal armed-response sidearm in the 1990s. The US FBI adopted the Glock 17M and Glock 19M in 2016 after the Smith and Wesson M+P failed qualification testing.

The SIG Sauer P226 (9x19mm, 15-round magazine) and P228/P229 use a DA/SA (double-action / single-action) hammer-fire system: the first shot fires double-action (long trigger pull from an uncocked hammer), subsequent shots single-action (short trigger pull from the cocked hammer). The P226 was adopted by the US Navy SEALs in 1989 and by numerous European police forces. The P226 firing-pin impression is round and centrally placed. The newer SIG P320 (introduced 2014, adopted by the US military as the M17 and M18 in 2017) is modular and striker-fired, with a serialised fire-control unit that can move between different grip modules and slide sizes.

The Beretta 92FS (9x19mm, 15-round magazine) employs an open-slide design where the forward third of the slide is cut away to expose the barrel, and a falling-locking-block system rather than Browning's tilting barrel. This open slide means the firing-pin impression is struck by a Beretta-specific external hammer. The Beretta 92FS was the US military M9 sidearm from 1985 through 2017. The Italian Carabinieri and Polizia di Stato both carry it. In forensic casework, the Beretta 92 series is distinguishable from Browning-pattern pistols by the locking-block wear marks on the case head and the specific shape of the Beretta external hammer firing-pin impression.

Semi-automatic pistols operate on one of two principles: locked-breech (recoil-operated, with Browning short-recoil or its variants the most common) or blowback (no barrel-slide lock, the slide is held closed only by spring tension and the inertia of the slide mass).

In a blowback pistol, the breech is not mechanically locked at the moment of firing. The slide is held closed only by the recoil spring and the mass of the slide itself. Blowback operation is inherently limited to lower-pressure cartridges because high chamber pressure would drive the slide rearward before the bullet has left the barrel, creating dangerous gas leakage. Blowback designs are therefore common in .22 LR, .25 ACP, .32 ACP (7.65mm Browning), and .380 ACP (9x17mm) calibres. The Walther PP and PPK (.32 ACP and .380 ACP), iconic in European civilian and police markets since 1929, are blowback-operated. The Beretta Tomcat (.32 ACP) and the Italian military's Beretta M1934 (.380 ACP) are blowback designs. The Czech CZ 82/83 (9x18mm Makarov) is a blowback pistol standard in Eastern European police inventories.

The Indian Ordnance Factories (IOF) produce two principal handguns for the domestic licensed-civilian market: the IOF .32 Pistol (also called the NPB .32, chambered for .32 S+W Long) and the IOF .380 Pistol Mk-IV (chambered for .380 ACP / 9x17mm). Both are blowback-operated, single-stack, hammer-fire designs derived from earlier European service pistol patterns. The IOF .32 is classified as Non-Prohibited Bore (NPB) under the Indian Arms Act 1959; the .380 Mk-IV similarly falls in the NPB category. A third IOF handgun, the Ashani pistol (introduced in 2020, also .32 calibre), is a more modern compact design produced at the Ishapore Rifle Factory. These three weapons appear frequently in Indian licensed-civilian homicide cases and custody-shooting inquiries; the examiner must have access to IOF test-fire reference samples, because the GRC (General Rifling Characteristics) of IOF barrels are not uniformly represented in the international databases maintained by the FBI and the BKA.

The Bundeskriminalamt laboratory in Wiesbaden conducted systematic comparison work on blowback pistols, including Walther PPKs recovered from Red Army Faction cases from 1972 onward. That casework contributed to BKA comparison protocols that informed subsequent ENFSI Firearms Working Group guidelines.

Locked-breech designs accommodate the higher-pressure cartridges used in full-power service calibres (9x19mm Parabellum, .40 S+W, .45 ACP, .357 SIG). The breech-face mark on a locked-breech case is deeper and better defined than on a blowback case, because the barrel and slide are mechanically coupled at the moment of peak pressure. For the comparison-microscopy examiner, this means locked-breech cases usually yield better striation detail on the case head and firing-pin impression than blowback cases, where the case moves slightly rearward before peak pressure is reached.

The comparison-microscopy protocol for a semi-automatic pistol case examines marks in the following order: firing-pin impression, breech-face marks, extractor marks, and ejector marks. Each set of marks has class characteristics (common to all weapons of the same make and model) and individual characteristics (specific to the particular weapon arising from machining, use, and wear).

The firing-pin impression shape is the first class discriminator. Glocks produce a round impression with a surrounding safety-plunger shadow ring. S+W M+P pistols produce a round impression. SIG P226 and P228 produce a round impression from an external hammer. Walther P99 and PPQ produce a round impression with a distinctive inner dimple. CZ 75 hammer-fire designs produce a round impression with a lighter rebound flattening at 6 o'clock from the rebounding hammer at rest. Older Browning P35 Hi-Power specimens produce a round impression with a distinctive starburst of firing-pin safety marks around the perimeter. These class characteristics allow a knowledgeable examiner to produce a hypothesis about the weapon type from the case alone.

The breech-face marks are striae left by the machined surface of the bolt face (slide face) as it slams forward onto the cartridge-case head during chambering and as it travels rearward under recoil with the case held against it. These marks are the primary individualising feature: because the breech face is machined and then worn uniquely, two pistols of the same model will leave different striation patterns, and these are what the comparison microscope directly resolves.

Extractor marks appear on the cartridge case rim at the 3 o'clock or 9 o'clock position (depending on which side the extractor is on) as a set of drag striations produced when the extractor spring snaps over the rim during chambering and as the extractor pulls the case rearward during extraction. Extractor-claw geometry is specific to each design and leaves a class mark.

Ejector marks appear on the case head face, typically at 6 o'clock, as a small impressed mark or gouge where the fixed ejector (a protrusion in the frame or slide) contacts the case head face and kicks the case out of the ejection port. The ejector mark is often the smallest and least defined of the four sets of marks, but it is useful for confirming which side the ejection port is on and whether the design uses a fixed or spring-loaded ejector.

In the United Kingdom, the National Ballistics Intelligence Service (NABIS), established in 2008, maintains a database of marks from fired cases recovered from crime scenes across England, Wales, Scotland and Northern Ireland. NABIS cross-references these marks against the INTERPOL Ballistic Information Network (IBIN) and the US NIBIN network via bilateral intelligence-sharing arrangements. A cartridge case recovered in Manchester, UK, can be cross-referenced against NIBIN entries from cases in Chicago or Toronto within hours under the NABIS-NIBIN-IBIN protocols. In India, the proposed Central Repository of Crime Scene Specimens under the DNA Technology Bill 2019 (not yet enacted) would create an analogous national database; at present, cross-case linking relies on manual examination at CFSL Chandigarh, CFSL Hyderabad, and state FSL laboratories.

India's domestic licensed-civilian handgun market is supplied almost entirely by the Indian Ordnance Factories organisation (now under the Ordnance Factory Board, part of the defence manufacturing ecosystem). Three production facilities contribute: the Gun and Shell Factory at Cossipore (Kolkata), the Ordnance Factory Khadki (Pune), and the Rifle Factory Ishapore (West Bengal).

The IOF .32 Pistol is chambered for the .32 ACP cartridge (7.65x17mmSR), a semi-rimmed straight-walled pistol cartridge standard in blowback semi-automatic designs. It is blowback-operated, single-stack (6+1 capacity), with an external hammer and a manual safety lever on the frame left side. The rifling is 6-groove, right-hand twist at approximately 1:10 inches, produced by button rifling at the factory. The headstamp on ammunition manufactured for it at IOF Khadki reads "KF" plus a two-digit year code. This pistol has been the principal NPB handgun available to licensed Indian civilians for decades, and it appears in a significant proportion of Indian licensed-owner homicide cases, accidental-discharge cases, and licensed-weapon theft cases.

The IOF .380 Pistol Mk-IV is chambered for .380 ACP (9x17mm), a rimless, slightly tapered case fired from a blowback-operated pistol with a 7-round single-stack magazine. The Mk-IV represents the fourth revision of the IOF .380 design lineage and incorporates an improved extractor and a revised magazine release compared to earlier marks. The rifling is 4-groove, right-hand twist. Both IOF .32 and .380 weapons share the characteristic of relatively unsupported breech-face marks that occasionally show partial case-head deformation from the blowback spring timing, a feature the examiner should note and not confuse with post-firing handling damage.

The Ashani pistol (Ordnance Factory Ishapore, introduced 2020) is a more compact .32-calibre design intended to replace the older IOF .32 in the licensed-civilian market. It shares the blowback, single-stack architecture but has a polymer grip frame, a more modern profile, and a redesigned manual safety. Forensic comparison reference specimens from Ashani pistols are held at CFSL Chandigarh and at CFSL Hyderabad; examiners encountering an Ashani case should verify that the test-fire reference is drawn from an Ashani specimen, not an earlier IOF .32, because the firing-pin and extractor geometry differ.

For any Indian handgun case, the examiner's report should state explicitly which reference collection was used for class comparison, whether from the CFSL GRC file, the Hyderabad or Chandigarh reference library, or a test-fire from the suspect weapon itself. This practice mirrors the requirement under SWGDAM guidelines in the US (that the examiner document the reference collection and state its source) and the Forensic Science Regulator's guidance in the UK (Codes of Practice and Conduct, section on firearms examination, 2020 edition), which requires documented provenance for every comparison reference used.

Handgun-type identification from cartridge-case marks is a sub-discipline of firearms examination governed by the same evidentiary frameworks as bullet striation comparison. Weapon-type classification from class characteristics is a lower-order inference than source-specific identification from individual characteristics, and courts have generally treated the former as less contested.

In the United States, firearms examination is admitted under the Daubert standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) in federal court, and under Frye or Daubert equivalents in state courts. The 2009 National Academy of Sciences report "Strengthening Forensic Science in the United States" and the 2016 PCAST report both questioned the error rates claimed for firearms examination, particularly for source-specific bullet and case comparison. Weapon-type inference from class characteristics, however, is less contested because the inference is at the class level: "This case was fired in a Glock-pattern striker-fire pistol" depends on observable class marks and does not require the same level of individualisation certainty as "this case was fired in this specific Glock 17."

In the United Kingdom, firearms examination evidence is admitted under the Criminal Procedure Rules and the expert-witness framework established in R v. Turner (1975, CA), with the Forensic Science Regulator's Codes of Practice and Conduct providing the operational quality standard. NABIS examiners prepare reports under the Forensic Science Regulator's guidance and must state the basis for any opinion, including the reference collection used for class comparison. Post-Daubert concerns have not triggered the same level of judicial scrutiny in English courts as in US federal courts, but the Criminal Procedure Rules Part 19 require the expert to state the substance of the facts and the reasoning supporting each opinion.

In India, firearms examination evidence is admitted under the Indian Evidence Act 1872 (now the Bharatiya Sakshya Adhiniyam 2023, § 45, expert opinion). Section 45 of the BSA 2023 mirrors the prior IEA § 45 in requiring that the expert possess "special skill" in the relevant field. The Supreme Court of India has accepted ballistic evidence in numerous cases; the Sanjay Dutt case (State v. Sanjay Dutt, 1993, relating to possession of an AK-56 and a 9mm pistol under TADA 1987) included ballistic evidence, and the Supreme Court's 2006 judgment upheld the conviction partly on the basis of this evidence. Indian forensic examiners report under the CFSL reporting format, which requires statement of the method, instruments used, comparison basis, and the scope of the conclusion (class level vs individualisation level).