1.
FIREARMS
BY SACHIN KUMAR TRIPATHI
MASTER IN FORENSIC SCIENCE
UNIVERSITY OF LUCKNOW

2.
FIREARMS
• Forensic analysis is vital
to solving a crime that
uses a gun.
• In 2004, there were 12,00
homicides in the US

3.
FIREARMS: A QUICK HISTORY
1. Almost every gun is based on the same simple concept: You apply explosive
pressure behind a projectile to launch it down a barrel.
2. The earliest & simplest application of this idea is the cannon.
3. The 1st handheld guns were essentially mini-cannons; you loaded some
gunpowder & a steel ball & lit a fuse

4.
4. War typically resulted in the need for improved weapons technology.
5. In the late 1800s, the revolver quickly became popular due to its size & quick
loading.
• It only had to be reloaded every 5-6 shots instead of
after each shot.

5.
6. Handguns reigned supreme for the past 200 years & to this day,
remain the most popular & readily available firearm.

6.
TYPES OF FIREARMS
1. Handguns (pistols)
– Revolver
– Semiautomatic
2. Rifles
3. Shotguns
4. Air or BB guns Handgun

7.
AMMUNITION
Components
1. Cartridge
case
2. Primer
3. Propellant
4. Projectile

8.
BULLETS
• Made of lead, sometimes
jacketed with brass,
copper, or steel
• Bullet size—diameter
(caliber or gauge)
• Shapes

9.
FIREARMS IDENTIFICATION
1. Often confused with the term ballistics
2. Ballistics is the study of a projectile in motion.
• Inside the firearm
• After it leaves the firearm
• When it impacts the target
3. Identification of Firearms is based upon this basic
idea: A harder object marks a softer one &
imparts/transfers its microscopic irregularities
to that object.

10.
FORENSIC FIREARMS EXPERT
1. Did a suspect use this gun to kill that
person?
2. Did these bullets come from that gun?
3. Was it really self-defense?
4. Is this a case of suicide, or is foul play
involved?
5. Bullet Comparison
6. Weapons Function
– Is it safe? Has it been modified?
7. Serial Number Restoration
8. Gunpowder Residue Detection
– on clothes, hands, & wounds
9. Muzzle-to-Target Distances

11.
PULLING THE TRIGGER
1. Pulling the trigger releases the firing pin…
2. The firing pin strikes the primer…
3. The primer ignites the gun powder…
4. The powder generates gas that propels the bullet forward through
the barrel & ejects the spent cartridge case.

12.
BULLET CALIBER
1. Caliber: the diameter of the gun barrel.
2. Caliber is recorded in
• hundredths of an inch (.22 & .38)
• millimeters (9mm)

13.
BULLET ANATOMY

14.
CARTRIDGE PARTS & HOW IT WORKS
Cartridge Parts and How it Works
Cartridge Case
Gun Powder
Lead Bullet
Primer

15.
ANATOMY OF A BULLET

16.
BULLET COMPARISONS
1. Each gun leaves distinct markings on a bullet passing through
it.
2. A gun barrel is made from a solid bar of steel that has been
drilled/hallowed out.
3. The drill leaves microscopic marks on the barrel’s inner
surface.
4. Gun manufacturers also add spiral grooves to the barrel. This
is known as rifling.
5. Lands: the space between the grooves.
6. As a spinning bullet passes through the barrel, it is marked by
these grooves.

17.
RIFLING
1. The grooved spirals inside
the barrel of a gun that
produce lands and grooves
on a bullet
2. Lands & grooves are class
characteristics

18.
STRIAE
1. Scratches on a fired bullet,
2. like a barcode
3. Can serve as individual
evidence
4. Matching bullets or bullets to
a firearm Scratch

19.
CLASS CHARACTERISTICS
1. Class Characteristics: Once a manufacturer chooses a
rifling process, for a particular class of weapon, they
keep it consistent.
2. Lands & Grooves are the same for a model.
• .32 caliber Smith & Wesson has 5 lands & grooves twisting to
the right.
• .32 caliber Colt has 6 lands & grooves twisting to the left.
3. Class characteristics can eliminate certain makes but are
not enough to ID a particular gun.

20.
INDIVIDUAL CHARACTERISTICS
1. Imperfections in the manufacturing process make each barrel
unique.
2. Rifled barrels, even if made in succession will NOT have identical
striation (scratch-like marks).

21.
BULLET COMPARISONS
1. To match bullets to a gun, test bullets
must be fired through a suspect barrel
for comparison.
2. Goddard & Comparison
• Examined bullets side-by-side (to
match striated markings).

22.
CARTRIDGE CASE
1. Usually brass
or nickel-clad
brass
2. Class evidence
– Manufacturer
– Shape
– Caliber
– Composition
Head Stamps
Rimfire & Centerfire Cartridges

23.
CARTRIDGE MARKINGS
1. All moving components contact the cartridge
rather than the bullet can leave useful
impressions on shell cartridges.
2. Cartridge Case Individual Characteristics:
• Breech face marks
• Firing pin impressions
• Chamber marks
• Extractor marks
• Ejector marks

24.
Breech
Extracting
Pin
Firing Pin
Ejector (not shown)

25.
BREECH MARKS
When a cartridge is fired, the explosion forces the
bullet down the barrel and the shell casing is forced
back against the breech. This leaves impressions
unique to the individual gun’s breech on the shell
casing.
Breech
1. When a cartridge is fired, the explosion forces the bullet down
the barrel and the shell casing is forced back against the
breech.
2. This leaves impressions unique to the individual gun’s breech
on the shell casing.

26.
BREECH FACE MARKS

27.
ACTUAL BREECH MARKS

28.
FIRING PIN MARKS
1. In order to fire the cartridge, the
primer must first be ignited. To
accomplish this a firing pin
strikes the center ring of the
cartridge.
2. This will in turn leave a distinct
impression that is unique to the
firing pin of that particular gun.
Firing Pin M
In
ca
mu
ac
pin
rin
Th
dis
is
of

29.
FIRING PIN MARKS

30.
CHAMBER MARKS

31.
EJECTOR MARKS

32.
EXTRACTING PIN & EJECTOR MARKS
1. The extracting pin and ejector
throw the spent shell casing from
the chamber of the gun.
2. These leave marks on the shell
casing that are unique to those
parts on that particular firearm.
Extracting Pin and Ejector Marks
The extracting pin
and ejector throw
the spent shell
casing from the
chamber of the
gun.
These leave marks
on the shell casing
that are unique to
those parts on that
particular firearm.

33.
OTHER FACTORS
1. Perfect matches are sometimes difficult b/c:
• Presence of grit & rust in a barrel
• Recovered bullets too mutilated or distorted on impact
2. A spent bullet’s weight can sometimes determine the gun’s
make.
3. Microgrooves: 8-24 grooves; it’s not as common
4. General Rifling Characteristics File
• FBI database of known land/groove width for all weapons.

34.
SHOTGUNS
1. Smooth barrel
– Projectile NOT marked as it passes through
2. Fire small lead balls or pellets
contained within a shell.
3. Characterized by:
– diameter of the shot
– size & shape of the wad
– Gauge: diameter of the barrel
( gauge  diameter)
4. Identification can still be made by
comparison of extractor/ejector
markings on the shotgun shell.

35.
FEATURES OF A SEMIAUTOMATIC HANDGUN

36.
FIREARMS EVIDENCE
Individual:
1. Stria
2. Firing pin marks
3. Breech marks
4. Extractor marks
5. Ejector marks
6. Chamber marks
Class:
1. Bullet type
2. Bullet caliber
3. Bullet weight
4. Lands and grooves
5. Rifling
6. Cartridge case
7. Head stamp

37.
GUNSHOT RESIDUE (GSR)
1. When a weapon is fired:
- Primer and propellant particles
blow back toward the shooter.
- Combustion products (mostly
NO2
-), unburned propellant, and
particles of lead follow the bullet,
spreading out with distance.

38.
1. GSR Sources:
• victim, clothing, or target
• shooter’s hands
2. Gunpowder Chemistry
• Major detectable elements are: lead (Pb), barium (Ba) &
antimony (Sb)
• Virtually all cartridge cases are made of brass (copper
& zinc); also detectable.

39.
GRIESS TEST
1. Tests for the presence of nitrates (partially burned or unburned
gunpowder)
2. Swab of the shooter’s hand
3. Must produce a pattern for a distance determination
• Test

40.
RESULTS OF GSR HAND TEST
1. Negative results may be caused by:
• Washing the hands
• Shooter may have been wearing gloves
• Lead-free ammunition
2. A rifle or shotgun may not deposit GSR on hands

41.
3. GSR ON THE HAND OF A SUICIDE VICTIM,
PROVING HE WAS HOLDING THE WEAPON
WHEN IT WAS FIRED.

42.
4. With contact or a very close-range gunshot wound, it is possible to
have blood spatter as well as GSR on the hand of the person firing
the weapon.

43.
CONTACT GUNSHOT WOUND
1. This is a contact gunshot
entrance wound.
1. Since the barrel contacts
the skin, the gases
released by the fired round
go into the subcutaneous
tissue & cause the star-
shaped laceration.

44.
ABRASION RING
1. An abrasion ring, formed when the
force of the gases entering below
the skin blows the skin surface back
against the muzzle of the gun, is
seen here in this contact range
gunshot wound to the right temple.
2. The abrasion ring, and a
very clear muzzle imprint,
are seen in this contact
range gunshot wound.

45.
ENTRANCE/EXIT
WOUNDS
3. This is a contact range gunshot
entrance wound with grey-black
discoloration from the burned
powder.
Displayed here is an entrance at the left and an exit at the right.
1. Exit wounds vary considerably in size and shape because
the bullet can be deformed in its transit through the
body.
2. There may be no exit wound at all if the bullet's energy
is absorbed by the tissues. Some bullets (such as a
"hollow point") are designed to deform so that all their
energy will be converted to tissue damage and not exit.

46.
4. Powder tattooing is seen
in this intermediate-
range gunshot wound.
The actual entrance site
is somewhat irregular
because the bullet can
tumble in flight.

47.
5. The surface of the skull demonstrates the heavy soot in
this contact range entrance wound, as well as radiating
fracture lines. The direction of fire was thus toward the
back of this picture.

48.
SERIAL NUMBER RESTORATION
1. When a serial number is stamped into a gun, the metal
underneath the number is compressed & hardened.
2. If the number is filed-off, the hardened area may still be
present.
3. By using an acid solution the metal can be slowly eaten
away.
• In this process the softer metal will be eaten away first and the number
may reappear.

49.
FIREARMS EVIDENCE COLLECTION
1. Make sure it is unloaded!!!!!
2. DO NOT put a pencil into a barrel
3. REVOLVERS
• Indicate the location of fired & unfired ammunition
4. AUTOMATICS
• Check the magazine for the number of rounds
• Fingerprint magazine
5. Place the ID tag on the trigger guard

50.
6. AMMUNITION
• Write on base or nose
• Package in pill box or envelope
• Wrap in tissue to protect

51.
7. CLOTHING
• Protect & preserve
any residue
• Air dry if wet
• Package separately
in paper bags
8. Establish CHAIN OF
CUSTODY