Intro to Firearms

FRSC 350 - Caryn Tucker

What are the three basic rules for firearm saftey?

1. Always keep the gun pointed in a safe direction

2. Always keep your finger off the trigger until ready to shoot

3. Alwyas keep the gun unloaded until ready use

What is a stereomicroscope?

Instrument that provides 3D viewing of an object through paired objectives and eyepieces.

What do stereomicrocopes allow for the analyst to do to the evidence?

Allows for moving, grabbing twisting, angling, and measuring the evidence.

What does the stereomicroscope bridge?

Bridges a regular visual examination with the comparison microscope analysis.

What are the two kinds of stereomicroscopes?

• Greenough (most common)

• Common Main Objective

What are characteristics of a Greenough stereomicroscope?

Rugged, inexpensive stereomicroscope with two identical optical systems offset to create the effect.

What are the characteristics of a Common Main Objective steromicroscope?

Stereomicroscope with one large objective lens that produces a collaminated light path.

What is a collimated light path?

Light rays travel parallel to one another with minimal divergence, meaning the beam stays narrow and concentrated over long distances.

Why are Greenough stereoscopes more common than CMO’s?

They are relatively cheaper.

What is a comparison microscope?

Essentially two microscopes connected to an optical bridge that allows the viewe to observe two objects at the same time in the same magnification.

What kind of view does the comparison microscope give?

A 2D comparison that showes detailed hills and valleys on the surface of the samples due to the oblique lighting.

What is the separating line in comparison microscopes called?

The prism line.

What is analyzed in comparison microscopes?

Fired ammunition.

What is the typical magnification of a comparison microscope?

5x or 10x occualrs.

Apart from comparison microscopes, what other tools are used in this kind of analysis?

Other measuring tools like: powder balances, trigger pull mechanisms,

What is a powder balance?

High precision balance used to measure the mass of a bullet and the powder inside of it.

What does the powder balnce aid in determining?

The caliber of a bullet.

What is the mass off the powder useful to know in?

Downloading cartridges, reloading/handloading cartridges.

What is a trigger pull mechanism?

A measuring device that helps measure the amount of force needed to pull a trigger, this force is typically measured in pounds.

What is trigger pull force determination usually used for?

By some agencies to determine internationality of pulling a trigger in ‘accidental’ cases.

How is trigger pulled measured? (2 ways)

1. Arsenal: weights are increasingly added until the trigger releases firing mechanism

2. Spring gauge: increasing amount of pressure applied until trigger releases firing mechanism

What is not considered in trigger pull that may be an effector in a case?

Momentum of the shooter.

What is a force gauge?

An automated model that recognizes when the trigger “breaks”.

What is force gauge measured in?

Joules.

What are two important important physical measurements of firearms?

1. Length of barrel

2. Overall length of firearm

What is the certification needed in measurements of firearms with linear measurements?

NIST standard.

What is the MINIMMUM length of a barrel in a short-barreled?

Eighteen inches.

What is the MINIMMUM full length of a short-barreled?

26 inches.

What is the MINIMMUM length of a barrel in a long-barreled?