(Discussion and Continue Worksheet - Firearms) Wednesday February 28, 2018 (Discussion and Continue Worksheet - Firearms)

The Daily CSI Wednesday, 2/28/18 None Today!

Remediation for Quiz 12 runs through Friday! Announcements Remediation for Quiz 12 runs through Friday!

Summative or Formative # Hold for eResearch Paper Assignment Summative or Formative # Date Issued Gone Missing Day Last Day Accepted QUIZ 12 S3 2/26 Friday WS – Firearms F11 2/27 N/A Hold for eResearch Paper

Firearms Projectiles

Shell Anatomy Handgun and Rifle Shotgun

Anatomy of a Bullet

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/hollowed out. The drill leaves microscopic marks on the barrel’s inner surface.

Bullet Comparisons Gun manufacturers also add spiral grooves to 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.

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.

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).

Bullet Comparisons To match bullets to a gun, test bullets must be fired through a suspect barrel for comparison. Comparison Microscopes Examined bullets side-by-side (to match striated markings).

Bullet Comparisons

Cartridge Markings All moving components contact the cartridge rather than the bullet can leave useful impressions on shell cartridges Breechface marks Firing pin impressions Chamber marks Extractor & Ejector markings

Breechface Marks

Actual Breech Marks

Firing Pin Marks

Chamber Marks

Ejector Marks

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.

Shotguns 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)

Continue Worksheet Firearms