#14 - firearms

Definition: A firearm is a device that launches projectiles, including bullets, using a controlled explosion.
Components:
- Projectile: The bullet itself.
- Barrel: The part of the gun through which the bullet travels.
- Bullet: The actual projectile that exits the firearm.
- Primer: A crucial component that ignites the powder.
- Flash Hole: A small hole that allows flame from the primer to ignite the powder.
- Powder: The explosive material that propels the bullet.

Composition:
- A mix of various metal-based compounds:
  - Lead: 2,4,6-trinitroresorcinate (also known as lead styphnate) is shock sensitive.
  - Antimony Sulfide: Acts as fuel (Sb2S3).
  - Barium Nitrate: Serves as an oxidant (Ba(NO3)2).

Post-Ignition Residue: The gases expand and cool, leaving residues containing:
- Lead (Pb)
- Antimony (Sb)
- Barium (Ba)
Other Elements: Includes aluminum (Al), sulfur (S), tin (Sn), calcium (Ca), potassium (K), chlorine (Cl), and silicon (Si).
Mercury Fulminate: Found in ammunition from Eastern Europe; utilized in specific regions of the Middle East.

Function: Primer ignition leads to combustion of the gunpowder.
Types:
- Black Powder: 75% KNO3 (oxidizer), 15% charcoal (fuel), 10% sulfur (fuel).
- Chemical Reaction: Produces gases and heat through combustion.

Components of Ammunition: Primer, powder, bullet, coating, metal jacket, cartridge case.
Materials Used:
- Cartridge Case: Typically brass (70% Cu and 30% Zn); may have a nickel coating.
- Bullet Cores: Mostly brass (90% Cu, 10% Zn); could be a ferrous alloy or aluminum.
- Coatings: Often contain nickel.

Advantages: High density (11.34 g/cc) and cost-effective.
Disadvantages: Softens at >1000 ft/s, leading to barrel smearing; melts at >2000 ft/s.
Solution: Use of a copper jacket to prevent smearing and enhance performance.

Structure: Contains grooves (rifling) and lands (raised ridges) that impart rotational motion to the bullet.
Types of Firearms:
- Pistols: Handguns
- Rifles: Longer-barreled weapons
- Machine & Submachine Guns: Automatic firearms.

Indirect Matching: Unique striations from the barrel help match bullets, but not directly between a bullet and a barrel.
FBI Records: Maintains the General Rifling Characteristics File for identifying class characteristics of bullets.

Firing Pin Impressions: Unique markings made by the firing pin on the primer show imperfections.
Breechblock Impressions: The cartridge case may show surface markings from the breechblock.

Matching Composition: Percent composition of recovered bullets can be compared to those in a box, though variations exist.
Analysis Methods: Spark Source Mass Spectrometry (SSMS) can differentiate bullet compositions.

Residue Identification: Consists of primer and powder; distance between barrel and target is important.
Initial Testing: Starting with swabbing the hands for GSR post-firing.

Dermal Nitrate Test: Hot paraffin applied to hands to check for nitrates; less reliable due to false positives.
Hand Swabs: Obtaining swabs from hands to analyze for residues within a 6-hour timeframe.
Adhesive Tape Method: Tape lifts residues for analysis.
Instant Shooter ID Kit: New method using swabs and reagents for rapid identification.

GSR Distribution: Helps assess firing distance from a victim.
- <1 inch: heavy lead concentration; signs of burning.
- 12-18 inches: vaporous lead halo.
- 3 feet: bullet wipe present; no powder residue.

Visual Inspection: Using microscope for residues.
Infrared Photography: Non-invasive analysis.
Chemical Tests:
- Modified Greiss Test for nitrites.
- Sodium Rhodizonate Test for lead confirmation.

Tests for lead presence; pink reaction indicates lead, blue confirms its presence.

Incident: Bombings in Birmingham, England, 1974; suspects tested positive for nitrites using the Greiss test.
Outcome: Evidence led to convictions, but the test’s reliability was later challenged due to potential contamination from common items.