BALLISTICS

The big picture of ballistics

Because every contact leaves a trace (Locard’s exchange principle) very hard contacts (like a 180 mps to 1500 mps contact) will leave a big trace

History of History of Gunpowder and Firearms Gunpowder and Firearms

The Chinese invented gunpowder over a thousand years ago.

Muzzle-loading matchlocks used wicks to ignite the gunpowder.

The cartridge and breech loading followed. Rifling provided greater accuracy. Revolver, semi-automatic, and automatic

handguns were developed.

BallisticsBallistics– TThe study of projectiles, trajectories, he study of projectiles, trajectories,

and the effect on the targetand the effect on the targetFirearms Identification

–A sub-discipline of ballistics that determining whether a bullet or cartridge was fired by a particular weapon

Introduction Introduction

Ballistic evidence helps explain: What type of firearm was used. The caliber of the bullet. The number of bullets fired. Where the shooter was. Whether a weapon was fired recently. If a firearm was used in previous crimes.

AA Internal ballisticsInternal ballistics

What happens in the weaponWhat happens in the weapon

BB External ballisticsExternal ballistics

What happens after the bullet leaves the What happens after the bullet leaves the barrelbarrel

CC Terminal ballistics (wound ballistics)Terminal ballistics (wound ballistics)

What happens when the bullet hits the targetWhat happens when the bullet hits the target

A Internal ballistics (1 of 3)

INTERNAL BALLISTICS

SO WHAT’S A CARTRIDGE?a combination of:

– a projectile (the bullet)– a propellant (gunpowder, for example)– a primer (the explosive cap),

A

Cartridges Design Cartridges Design

The bullet, usually made of metal, is out front with the cartridge, holding the primer and propellant powders, behind.

Watch this short video

http://www.youtube.com/watch?v=c1VD1D1hLsQ

How a gun Works

1. The firing pin hits the base of the cartridge, igniting the primer powder.

2. The primer powder sparks through the flash hole to the main propellant supply.

3. The pressure of the explosion pushes the bullet from the case into the barrel.

4. The bullet follows the lands and grooves spiraling out of the barrel.

Land = highGroove = Low

BACK OF BULLET

A BROACH CUTTER USED TO CREATE RIFFLING IMPRESSIONS IN A BARREL

As a result of rifling, a barrel will impress a negative impression of itself on the sides of the bullet like those seen below. 

A

Matching impressions

A

A fired bullet as class evidence

Different gun manufacturers use different rifling techniques. These techniques impart the class characteristics on a fired bullet.– Number of impressions– Width of impressions– Depth of impressions– Angle of impressions

Q: How are these 2 guns different

A: caliber

What is caliber? Caliber = the diameter of the bullet. Measured in hundredths of an inches.

– .22, .357, or .50

Measured in metrics– 9mm

Question: Why should the caliber of ammunition match the firearm that shoots it? If they do not match, what could go wrong?

A

Showing variation within caliber

INTERNAL BALISTICS (2 OF 3)

BREECH MARKS ARE FOUND ON THE REAR OF A FIRED CARTRIDGE

A

A

Firing pin

Breech

A

When a bullet is fired, the explosion forces:

1. the bullet down barrel

2. the cartridge back against breech– Leaving a negative impression on the back of

the cartridge

Depending on the make of gun & normal wear and tear, the breech markings will pick up class, and hopefully, individual characteristics.

Examples of breech markings

How CSI determines if a recovered bullet from a crime scene came from a suspected gun

http://www.youtube.com/watch?v=3EJrbpg43qM

Disclaimer: this video is oooooold

Shotguns have smooth barrels with no rifling.– Are there lands or groves on the bullet(s)?

How can a F.S. identify trace evidence left by a shotgun?– Only by marks on the spent shell casing(s):

Shotgun into ballistics gel

B

EXTERNAL BALLISTICS

External ballistics is everything that happens after the bullet leaves the gun to just before the BULLET impacts its target

GUN SHOT RESIDUE

GUN SHOT RESIDUE (GSR)

CAN BE DETECTED EVEN AFTER WASHING CLOTHING / HANDS

Gunshot ResiduesGunshot Residues Particles of unburned powder and traces

of smoke are the residues of gunshots. They can leave a trace on:

– Shooterhand, arm, face, hair, or clothing

– Victim Chemical testing often can detect residue

even if removal is attempted. The distance from the victim to the

shooter can be determined by examination of the residue pattern on the victim.

Trajectory Trajectory

Path of bullet

Horizon

Wind shield

Distance along path of bullet to window, 23.9”

Distance along horizon to window, 23.5”

yx

60 feet

TrajectoryTrajectory

2 Reference points needed to determine trajectory

– can be bullet holes in objects or victims.

Investigators can use lasers to trace a straight-line path to help determine the position of the shooter.

http://www.glenbrook.k12.il.us/

http://www.glenbrook.k12.il.us/

External ballisticsExternal ballistics

Point of initial Point of initial intersectionintersection

Maximum ordinateMaximum ordinate

Point of secondary Point of secondary intersectionintersection

Point of impactPoint of impact

Point of aimPoint of aim

5 Ballistic Terms5 Ballistic Terms PII – Point of Initial Intersect. Where the bullet crosses the PII – Point of Initial Intersect. Where the bullet crosses the

LOS (Line of Sight) for the first time.LOS (Line of Sight) for the first time.

MO – Maximum Ordinate. The highest point the bullet MO – Maximum Ordinate. The highest point the bullet reaches during its parabolic flight path.reaches during its parabolic flight path.

PSI – Point of Secondary Intersect. The point where the PSI – Point of Secondary Intersect. The point where the bullet crosses the LOS for the second time.bullet crosses the LOS for the second time.

POI – Point of Impact. The point where the bullet impacts the POI – Point of Impact. The point where the bullet impacts the target.target.

POA – Point of Aim. Where the shooter was aiming the POA – Point of Aim. Where the shooter was aiming the weapon.weapon.

If the sights are properly adjusted:If the sights are properly adjusted:

POI = POA = DOA (dead on arrival)POI = POA = DOA (dead on arrival)

CC Terminal ballistics Terminal ballistics

Bullet WoundsBullet Wounds

1. Why do entrance wounds tend to be smaller than exit wounds?

2. If the bullet penetrates clothing, what can fibers embedded in the wound indicate?

3. Where is gunshot residue usually found?

4. If the gun is fired with the muzzle touching the victim’s skin, what telltale mark may show up?

5. Will larger or will smaller caliber bullets tend to lodge within the body rather than passing through? Why?

GUN SHOT RESIDUE

Bullet wounds (4 kinds)

1. Barrel on skin

2. Barrel just off skin

3. Barrel inches away

4. Shot from a distance

Notice:Distinctive star pattern, so…

energy from the gun shot forced back out entryway “blowback”

NO burnt gun powder marks around entryway, so…

•ALL gunpowder delivered inside entryway singing the interior (black area)

Barrel on skin

Barrel inches awayNotice:“stippling” of

the burning powder around the actual bullet entry way

No star pattern– No “blow back”

Barrel just off skinNotice: - no star pattern so..

– not ON skinNo stippling from g.p. so..

– TOO close for inches awayBarrel burns like on skin

so….– JUST off skin

Conclusion = shot from distance (probably through clothes)

9mm to person’s back NOTICE:– Lack of burnt gun powder burns on skin– Lack of star pattern

THE END

Shot from distance (but photo shopped)