Firearms

1. Firearms • Forensic analysis is vital to solve a crime that uses a gun. • In 2004, there were 12,00 homicides in the US The vast majority of U.S. homicides involve guns. And they are more powerful than ever. Lansing State Journal, July 2007

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

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

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

5. Types of Firearms • Handguns (pistols) • Revolver • Semiautomatic • Rifles • Shotguns • Air or BB guns

6. Ammunition Components • Cartridge case • Primer • Propellant • Projectile

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

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

9. Forensic Firearms Expert • Did a suspect use this gun to kill that person? • Did these bullets come from that gun? • Was it really self-defense? • Is this a case of suicide, or is foul play involved? • Bullet Comparison • Weapons Function • Is it safe? Has it been modified? • Serial Number Restoration • Gunpowder Residue Detection • on clothes, hands, & wounds • Muzzle-to-Target Distances

10. Pulling the Trigger • Pulling the trigger releases the firing pin… • The firing pin strikes the primer… • The primer ignites the gun powder… • The powder generates gas that propels the bullet forward through the barrel & ejects the spent cartridge case.

15. How a Revolver Works - YouTube.wmv • HOW A GUN WORKS - YouTube.wmv • How A Glock Works - YouTube.wmv

16. Bullet Caliber • Caliber: the diameter of the gun barrel. • Caliber is recorded in • hundredths of an inch (.22 & .38) • millimeters (9mm)

17. Bullet Anatomy

18. Cartridge Parts & How it works

19. Anatomy of a Bullet

20. Bullet Comparisons • Each gun leaves distinct markings on a bullet passing through it. • A gun barrel is made from a solid bar of steel that has been drilled/hallowed out. • The drill leaves microscopic marks on the barrel’s inner surface. • Gun manufacturers also add spiral groovesto the barrel. This is known as rifling. • Lands: the space between the grooves. • As a spinning bullet passes through the barrel, it is marked by these grooves.

21. Rifling • The grooved spirals inside the barrel of a gun that produce lands and grooves on a bullet • Lands & grooves are class characteristics

22. Striae • Scratches on a fired bullet, • like a barcode • Can serve as individual evidence • Matching bullets or bullet to a firearm

23. Class Characteristics • Class Characteristics: Once a manufacturer chooses a rifling process, for a particular class of weapon, they keep it consistent. • 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. • Class characteristics can eliminate certain makes but are not enough to ID a particular gun.

24. Individual Characteristics • Imperfections in the manufacturing process make each barrel unique. • Rifled barrels, even if made in succession will NOT have identical striation (scratch-like marks).

25. Bullet Comparisons • To match bullets to a gun, test bullets must be fired through a suspect barrel for comparison. • Goddard & ComparisonMicroscopes • Examined bullets side-by-side (to match striated markings).

26. Cartridge Case • Usually brass or nickel-clad brass • Class evidence • Manufacturer • Shape • Caliber • Composition Head Stamps Rimfire & Centerfire Cartridges

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

29. 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.

30. Breech face Marks

31. Actual Breech Marks

32. Firing Pin Marks • 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. • This will in turn leave a distinct impression that is unique to the firing pin of that particular gun.

34. Firing Pin Marks

36. Chamber Marks

37. Ejector Marks

38. Extracting Pin & 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.

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

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

41. Features of a Semiautomatic Handgun

42. Firearms Evidence Individual: • Striae • Firing pin marks • Breech marks • Extractor marks • Ejector marks • Chamber marks Class: • Bullet type • Bullet caliber • Bullet weight • Lands and grooves • Rifling • Cartridge case • Head stamp

43. Gunshot Residue (GSR) • 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.

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

45. Griess Test • Tests for the presence of nitrates (partially burned or unburned gunpowder) • Swab of shooter’s hand • Must produce a pattern for a distance determination

46. Results of GSR Hand Test • Negative results may be caused by: • Washing the hands • Shooter may have been wearing gloves • Lead free ammunition • A rifle or shotgun may not deposit GSR on hands

49. GSR on the hand of a suicide victim, proving he was holding the weapon when it was fired.

50. With a contact or 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.