Topic 3 - Forensic Analysis of Ammunition

Question 1

How is ammunition size described?

Answer 1

By chambering and caliber

Question 2

What does caliber refer to?

Answer 2

The diameter of the projectile (typically the first number)

Question 3

What does chambering refer to?

Answer 3

The length of the cartridge (typically the second number)

Question 4

What can happen if you use the wrong size round?

Answer 4

A wrong-sized round will rupture and cause a shock front to impact the chamber which could lead to a rapid failure of the chamber/breech area

Question 5

What can you usually find on the base of the cartridge?

Answer 5

The head stamp

Question 6

What information might you get from the headstamp?

Answer 6

• Firing pin marks
• The end-user
• The calibre
• The manufacturer

Question 7

What rim do self loading firearms have and why?

Answer 7

• They have a normal base rim
• They must have parallel sides to allow them to stack in a magazine

Question 8

What type of rim do single-shot mechanisms, such as revolvers, have?

Answer 8

• They have a protruding base
• The protruding base stops the cartridge from falling through the cylinder

Question 9

What are some examples of class characteristics?

Answer 9

• General dimensions
• Caliber
• Chamber
• Shape of firing pin mark
• Primer type
• Headstamp information

Question 10

What characteristics are cartridge marks?

Answer 10

Individual

Question 11

What are typical cartridge marks?

Answer 11

• Ejection port dent
• Chamber marks
• Magazine lip marks
• Extractor lip marks
• Breech face marks
• Ejector mark
• Firing pin impression
• Firing pin scrape mark
• Slide scuff mark
• Slide drag mark

Question 12

What is a bullet?

Answer 12

• Basically, any projectile below about 20 mm in diameter that is fired from a barrelled weapon. Above this, it is a ‘shell’.
• Normally has a lead core
• The core is often surrounded by a gilding metal jacket. Gilding metal is a form of brass with a much higher copper content than zinc.

Question 13

What are the typical velocities for handgun bullets?

Answer 13

200-400 m/s

Question 14

What is the typical velocity for rifle bullets?

Answer 14

300-1500m/s

Question 15

What is the typical velocity for rifle bullets?

Answer 15

300-1500m/s

Question 16

What is the purpose of antimony in the bullet?

Answer 16

The antimony (Sb) reduces the malleability of the alloy and makes the lead core less easily deformed.

Question 17

When are unjacketed bullets used?

Answer 17

In low velocity applications

Question 18

What does jacketing stop?

Answer 18

• Jacketing stops ‘rifling drag’ in the barrel at
  higher velocities.
• Lead is so soft that the bullet skids over the
  rifling rather then engaging with it.
• Lead also deforms readily under acceleration.
• A gilding metal jacket improves rifling pick-up,
  and reduced acceleration deformation.

Question 19

What are the features of an unjacketed bullet?

Answer 19

• Lead alloy only
• May be round, flat or hollow nosed
• Cheap
• Low muzzle velocity so low penetration and high impact deformation
• Prine to rifling smear at high muzzle velocities

Question 20

What are the features of semi-jacketed bullets?

Answer 20

• Can be soft point, hollow point or polymer tipped
• Usually bright gilding metal with a metal alloy core
• Less impact deformation
• Low penetration
• High energy transfer

Question 21

What are the features of fully jacketed bullets?

Answer 21

• Usually a bright bass jacket with a bonded or partitioned lead alloy core
• The base can still have exposed lead
• Excellent penetration with relatively low energy transfer
• High stability
• High energy retention
• More expensive

Question 22

What does a partitioned core do?

Answer 22

Mushrooms and retains some of its core upon impact