Firearms and Ammunition

3 basic components of a firearm- barrel, ignition(hammer), trigger

Goals of firearm improvement- Speed,Distance, Accuracy

Differences between types of firearms- 

Revolver - holds 6-8 bullets, loaded manually in cylinder, single action (pull back hammer) or double action (hammer moves automatically), rifled barrels (lands +grooves), first commonly used handguns 

Semi-automatic - holds 10-15 rounds, ammunition in magazines, casing automatically extracted after firing (extractor marks), rifled barrels

Shotguns - smooth barrel, fires pellets, uses gauge for diameter of barrel (lower the gauge, larger diameter, amount of gauge = 1 pound, 12 gauge > 20 gauge) 

Rifles - rifled barrel, distance shooting, fires bullets

Bullets - used in handguns/ rifles, casing primer propellant projectile

Pellets - used in shotguns, primer casing pellets wad. 

Differences between types of gunpowder- black powder, smokeless single base, smokeless double base

1. Black Powder

• Made of charcoal, sulfur, and potassium nitrate.

• Produces a lot of smoke and residue.

• Low power compared to modern powders.

• Used in old guns, cannons, and fireworks.

2. Smokeless Powder (Single-Base)

• Made mostly of nitrocellulose.

• Burns cleaner with little smoke.

• More powerful than black powder.

• Used in most modern firearms.

3. Smokeless Powder (Double-Base)

• Made of nitrocellulose + nitroglycerin.

• Burns even faster and hotter.

• More powerful than single-base powder.

• Used in military and high-performance ammo.

Ammunition composition- Know Components and be able to draw

• Pistol(handgun)/rifle- primer, cartridge case, gunpowder, bullet

• Shotguns- primer, cartridge case, gunpowder, wad, pellets (birdshot, buckshot)

Bullets- class characteristics- caliber, manufacturer, composition, round nose/hollow point, center fire/rim fire, direction(right/left) of twist, degree of twist

Individual characteristic- striation pattern!

Firearm class characteristics- type of gun, manufacturer, caliber, rifling present/absent, # lands & grooves, width of lands/grooves, firing pin impression appearance, extractor marks (semi & automatic), twist ratio

Primer components- lead styphnate, barium nitrate, antimony sulfide

Propellants/Gunpowders- Black Powder, Single base, Double base

Components of gunshot residue- particles of explosive primer(burnt & unburnt) propellant, components of bullet, casing and firearm

Tests for gunshot residue- how they work/what they detect-

Positive Control vs. Negative Control, why use controls?

- Presumptive- Modified Griess Test (diphenylamine) - tests for nitrates, nitrites, chlorates, and perchlorates. colorless -> blue/black = positive result

- sodium rhodizonate - tests for lead in the primer, orange -> pink = positive result, possible false positives 

-  Confirmatory- SEM, NAA, AAS- elements detected (lead, antimony, lead) , appearance, size (1-10 micrometers), bright white, spherical

Scanning Electron Microscopy (SEM)

• What it does: Uses electrons to create high-resolution images of a sample’s surface.

• Best for: Looking at detailed textures and tiny structures (like bacteria, metals, or biological samples).

• Strengths: Provides 3D-like images, great for analyzing shape and composition.

• Weaknesses: Doesn’t give precise chemical composition; requires a vacuum environment.

2. Neutron Activation Analysis (NAA)

• What it does: Bombards a sample with neutrons, making elements radioactive so their identity and amount can be measured.

• Best for: Detecting trace elements in a material (used in forensics, archaeology, and nuclear science).

• Strengths: Very accurate, works on solid, liquid, and gas samples, and doesn’t destroy the sample.

• Weaknesses: Needs a nuclear reactor, expensive, and time-consuming.

3. Atomic Absorption Spectroscopy (AA)

• What it does: Uses light absorption to measure the amount of a specific metal in a sample.

• Best for: Detecting and measuring metals in water, blood, or food.

• Strengths: Highly sensitive for metals, simple, and relatively low-cost.

• Weaknesses: Can only detect one element at a time and needs a liquid sample.

Patterns of gunshot residue- cone shape creates circular patterns when residue hits an object/person- wider the circle, the greater the distance between the shooter and target 

Instrument for analyzing ammunition- comparison microscope- what is it and how does it work? 

A comparison microscope is a tool that lets you look at two things side by side at the same time. It’s used in forensics to compare bullets and casings.

How It Works:

1. Two microscopes are connected by a special bridge.

2. Each microscope looks at a different bullet or casing.

3. The images are shown side by side in the same eyepiece.

4. Experts check for matching marks (like scratches or grooves) to see if bullets were fired from the same gun.

Why Is It Used?

It helps crime investigators match bullets to a specific firearm, solving crimes.

Firearm/bullet database- NIBIN