Firearms Midterm

What is toolmark identification?

Discipline in forensic science where the primary concern to determine if a toolmark was produced by a particular tool

What is firearms identification?

Discipline of forensic science which has as its primary concern to determine if a bullet, cartridge case, or other ammunition component was fired by a particular firearm

This type of mark occurs when force and motion are parallel to the surface being marked.

Striated

What is the part after the "green parts" called?

"Brown parts" after the first bath. Brown parts are then moved to a sintering furnace to remove secondary binder and fuse the metal particles. Once fused, parts undergo finishing process

What are the diameter and weight of a .22 caliber class bullet?

.220" diameter, weight is ~40 grains

What are the diameter and weight of a .30 caliber class bullet?

.300"-.308" diameter, weight is ~123 to 220 grains

What are the diameter and weight of a .32 caliber class bullet?

.320" diameter, weight is ~71 to 98 grains

What are the diameter and weight of a .38/9mm caliber class bullet?

.355"-.363" diameter, weight is ~95 to 158 grains

Diameter of .355" would be which caliber class?

.38

What are the diameter and weight of a .40/10mm caliber class bullet?

.400" diameter, weight is ~165 to 180 grains

What are the diameter and weight of a .45 caliber class bullet?

.450" diameter, weight is ~230 grains

One of the most common rifling combinations is?

6 right

What is the firearm length for a handgun, revolver or pistol by CT State Statutes?

A barrel length of under 12"

What are the "levels of inconclusive" for bullet comparison?

A. Agreement of all discernible class characteristics and some agreement of individual characteristics, insufficient for an identification. B. Agreement of all discernible class characteristics without agreement or disagreement of individual characteristics due to an absence, insufficiency, or lack of reproducibility C. Agreement of all discernable class characteristics and disagreement of individual characteristics, but insufficient for an elimination

The theory of identification used by firearms and toolmark examiners is the:

AFTE Theory of Identification

How does honing work?

After reaming, surface can still be a little rough, a hone can help to smooth out any rough areas

Who was the first to use the comparison microscope for forensic application?

Albert S. Osborn

Who developed the optical bridge?

Alexander Von Inostrazeff

Define firearms

An assembly of a barrel and action that fires a projectile(s) via the products of combustion

Which rifling process uses a rod bearing 25 to 30 hardened steel rings of increasing size to cut into the bore?

Broach

Disadvantages of broach cutting?

Broaches take more skill to manufacture and the cutting edges are susceptible to chipping thus causing defect in the rifling

Which manufacturing technique can be used to make a breechface?

Broaching

What is the firearm length for a rifle by CT State Statutes?

Barrel must be at least 16" with an overall length of at least 26"

What is the firearm length for a shotgun by CT State Statutes?

Barrel must be at least 18" with an overall length of at least 26"

What are the parts of a revolver?

Barrel, cylinder, trigger, frame, hammer and sights

What does weight have to do with bullets?

Different calibers have ranges of different weights, measured in grains, listed on ammunition boxes

What are some cartridge case class characteristics?

Caliber (marked on headstamp), breechface marks (circle, arch, parallel, etc), firing pin impression shape (hemispherical, elliptical, rectangular), firing pin aperture shear, firing pin drag, location of ejector marks and location of extractor marks

What are the new parts from MIM called and how are they used?

Called "green parts" because they contain all the components of original feed stock. Green parts submerged in a liquid that removed primary binder.

Which rifling process is a swaging technique which uses a plug of extremely hard material bearing a negative impression of the rifling?

Button

How does button/swaging work?

Button rifling is a swaging technique, uses plug or button made of hard material bearing a neg impression of rifling. Plug is hydraulically pressed through the bore of barrel, stretching the inside diameter and imparting rifling characteristics. Button slightly larger than bore diameter. Cold working metal causes it to be harder but with more stress on the metallic structure

What are some class characteristics of bullets?

Diameter at base, number of lands and grooves, direction of twist, type of rifling (conventional vs polygonal), land and groove diameter and caliber

How does the chamber manufacturing technique work?

Chamber is part of the firearm that contains cartridge before it is fired. Can be the end of the barrel as in a pistol or part of the cylinder as in a revolver, machined using reamer, marks left behind in the chamber from manufacturing process may be left on outside of cartridge

Marks on the side of the cartridge case includes:

Chamber marks, magazine lip marks, ejection port marks

How does broach cutting work?

Common type rifling system that consists of a rod bearing 25 to 30 hardened steel rings each being slightly larger than the one before. Steel rings have notches cut into them that correspond to the dimensions of the rifling. As broach is pulled through the barrel all of the grooves are cut to the proper depth in on pass of the broach.

How do you measure land and groove diameter?

Comparison microscope

If a lathe is used to make a firing pin, what type of marks might occur in the firing pin impression?

Circular

If milling is used to make a breechface, what type of marks might occur on the cartridge case primer?

Circular

What marks will the filing/grinding portion of the breechface manufacturing technique leave?

Cross-hatch marks

What is the "Land-Grooveian" Theorem?

D=#(L+G)/pi

How is the item of evidence documented?

Describe all features observed (caliber, material, markings, etc.), mark evidence with case number, item number and initials, review notes, take into account items with similar class characteristics

What is electrochemical machining (ECM)?

Dissolves metal into desired shape. Brass is used as negative terminal and work piece as the positive. When submerged into solution of electrolytic salts, and electrical current is passed through the solution. Areas where the work piece is touching the brass will dissolve. Very effect means of machining, limits tool wear.

Which manufacturing technique creates the initial hole in the bar stock?

Drilling

What does the barrel manufacturing technique consist of?

Drilling, sizing, honing, rifling, lapping, profiling the barrel and crowning the barrel

This conclusion is appropriate when two items were not fired by the same firearm due to a difference of class or individual characteristics.

Elimination

How do you determine the direction of twist?

Examine a bullet from the base

Firing pin drag occurs when the primer is scraped along the aperture (hole) for the firing pin in the breechface. True or false.

False

Firing pin impression shape is a class characteristic for bullets.

False

True or False: Tools do not change over time with use

False

How does the filing machining technique work?

Finishing technique used to deburr freshly cut edges. Files usually hand worked and shaped to easily fit into small areas. The cutting edge of a file has teeth that are oriented such that they cut on the push stroke.

How are striated microscopic markings formed?

Force and motion parallel to surface being marked

How are impressed microscopic markings formed?

Force and motion perpendicular to the surface being marked

How are impressed-striated microscopic markings formed?

Force and motion perpendicular to the surface being marked but the surface is striated

What are the parts of a handgun?

Frame, slide, trigger, sights, barrel and magazine

When a firearm will discharge multiple cartridges with a single pull of the trigger it is what type of weapon?

Full automatic

How does the turning machining technique work?

Generally performed on a lathe. The workpiece is rotated while a cutter is moved back and forth horizontally. Considered an external cutting process

What makes a firearm a revolver?

Has a cylinder with multiple chambers that revolve around a central axis

What makes a firearm a rifle?

Has a rifled barrel designed to be fired from the shoulder

What makes a firearm a shotgun?

Has a smoothbore that is designed to be fired from the shoulder

Which rifling process uses a mandrel containing a negative impression of the rifling and hammers to impress the rifling into the barrel?

Hammer Forging

Types of firearms

Handguns, long guns, other-NFA firearms

How is the 3D view of comparison microscope used?

Has two objectives and two optical paths slightly off set so that each eye receives a different view under the scope. Allows for depth perception.

This conclusion is appropriate when two items were fired by the same firearm based on sufficient agreement of individual characteristics.

Identification

What are the four conclusions a firearm/toolmark examiner can come to?

Identification, inconclusive, elimination and unsuitable

This type of mark occurs when force and motion are perpendicular to the surface being marked.

Impressed

What does forensis mean?

In open court, public

What are some steps of the bullet examination process?

Ogive, nose, base, bearing surface, meplat, bullet type, jacket type, base diameter, weight, number of lands and grooves, direction of twist (left or right), type of rifling (conventional or polygonal), land and groove diameter and caliber determination

This conclusion is appropriate when two items cannot be identified or eliminated from having been fired by the same firearm.

Inconclusive

When is the AFTE theory in agreement?

It exceeds toolmarks made by different tools and it is consistent with agreement of toolmarks made by the same tool

Which manufacturing technique smooths out the bore?

Lapping

Which manufacturing technique can be used to make a firing pin?

Lathe turned

How are firing pins manufactured?

Lathe turned, MIM, stamped or milled. Lathe turned will have circular marks, MIM will have line in the middle of the firing pin impression, a stamped pin can by manufactured by placing a sheet of metal between a tool and a die to stamp out the part (used when firing pin is rectangular or flat), milling can be used to produce firing pin that is rectangular or flat

How does lapping work?

Lead lapping is a process that uses lead plugs impregnated with lapping compound to smooth out interior of bore

How does does the metal injection molding (MIM) machining technique work?

MIM has parts formed by combining finely ground metallic powder, primary binder and secondary binder. The materials are mixed and extruded into long thin wires fed into a press to form the shape of the part.

Advantages to broach cutting?

Make many more barrels in the same time it would take rifle using the hook method and there is less wear to the tool because there are more cutting edges

How does the swaging machining technique work?

Metal working process that uses dies to create desired shape. Type of foraging process because it applies compressive force to metal workpiece.

How are extractors and ejectors manufactured?

Milled (straight, parallel toolmarks), MIM (dividing lin in the middle) and stamped (used to make flat/rectangular parts)

Which manufacturing technique can be used to make an ejector?

Milling

What does the unsuitable conclusion mean?

No markings that would result in any of the previous conclusions (i.e. bullet core)

Features of the modern comparison microscope.

Objectives, eye pieces, stages, table (electronic), bridge adjustment, light sources (fiber optic, LED, fluorescent), mounting units (bullets, cartridge cases, toolmarks, wax), camera and software, measuring devices (stage micrometers, objective micrometers, software measuring abilities)

What is slippage on bullets?

Occurs between the land and groove impressions and is from the edge of rifling. Slippage is unique and can be used for identification

Where do ejector marks occur?

On the headstamp of the cartridge case, sometimes in the primer

Where do extractor marks occur?

On the rim and in the groove of the cartridge case

Where do ejection port marks occur?

On the side of the cartridge case

How is the 2D view of comparison microscope used?

One optical path through the objectives to the eye allowing for only one viewing position at a time

What are the base descriptions for a bullet?

Open/jacketed and flat/concave

Who was the first to use the comparison microscope for forensic work?

Osborn

Who adapted the stages of comparison microscopes to accept bullets?

Philio O. Gravelle

How is outer packing documented?

Photos and notes, mark packaging with case number, item number and initials

Which firearm typically has a magazine? Revolver or pistol?

Pistol

The two main categories of handguns are:

Pistols and revolvers

Types of handguns

Pistols and revolvers

Which firearm has a cylinder?

Revolver

How does drilling work?

Process in which a tool creates a hole in the stock, leaves parallel marks running perpendicular to long axis of the hole

How does sizing the bore work?

Reaming and broaching, reaming increases the inside diameter of the barrel to the proper caliber, manufacturers can also broach inside diameter

What does crowning the barrel do?

Recessing the rifling at the muzzle

What are the firing pin shapes?

Rectangular, hemispherical (circular) and elliptical

How is inner packaging documented?

Sub-itemized if needed (001-1)

How does the abrasive machining process machining technique work?

Refers to all sorts of machining processes that use abrasive materials to finish or refine metal parts (honing, lapping, lead lapping, grinding, sanding), randomly applied aggregate is conducive to individual markings

Types of long guns

Rifles and shotguns

What does rifling consist of?

Scrape/hook, broach cutting, button/swaging, hammer forging and electrochemical rifling

How does scrape/hook rifling work?

Scraping type of cutter consists of a rod slightly smaller than bore diameter with set of one or two hardened steel scrapers, each pass of the cutter some metal is removed. At the top of each stroke a small wedge is driven in just a small amount. Raises cutting surface enough to continuously remove metal with each stroke

The theory of identification allows an examiner to form an opinion of common origin when toolmarks are in:

Sufficient agreement

When a firearm will discharge one cartridge with a single pull of the trigger it is what type of weapon?

Semi-Automatic

How does the electro-discharge machining (EDM) machining technique work?

Sends an arc of electricity from an electrode (cutter) to the work piece. The arc of electricity created temperatures over 12,000 degrees Celsius and vaporizes the metal, useful for creating small and very accurate cuts

What is the conventional (standard) cut?

Sharp well-defined shoulders of groove impression

What are some NFA weapons?

Short barrel rifles or shotguns, full auto firearms, zip guns, home made weapons and unconventional weapons (cane guns, pen guns, etc.)

Which firearm has a smoothbore?

Shotgun

The two main categories of long guns are:

Shotguns and rifles

How does the boring machining technique work?

Similar to turning, utilizes stationary cutting tool and rotating work piece. Enlarges drill holes from the inside of the work piece. Usually considered internal cutting process

Which manufacturing technique increases the inside diameter of the barrel to the proper caliber?

Sizing

What is the polygonal cut?

Smooth rounded shoulders of the groove impression

What are all of the breechface marks?

Smooth, granular, cross-hatch, arch and parallel marks

How does the breechface manufacturing process work?

Some techniques used are broaching, milling and filing/grinding

What is NOT a firing pin shape?

Star

How does hammer forging work?

Swaging technique. Bored barrel blank placed over short mandrel that bears neg of the rifling impress (just like button). At barrel blank advances over mandrel, hammers pound outside of barrel and impart rifling impressions to interior of barrel. First attempts at hammer forging rifling often used larger mandrel which got stuck inside barrel after rifling. Shorter mandrels used because easier to manipulate. Profile of hammer forged barrels polygonal rifling. Curved sides of grooves shoulders allowed mandrel to be more easily removed

Define science

Systematic study of the structure and behavior of the physical and natural world through observation and experimentation

How do you determine the caliber of a bullet?

Take into account all measurements to determine the caliber of a fired bullet

What makes a firearm a pistol?

The chamber is integral to the barrel, can be semi-automatic or fully automatic

When is MIM used?

To manufacture small parts like extractors, ejectors and firing pins

What makes differences in pieces of metal?

The arrangement of atoms in the crystal structure and the impurities or additives

How does the barrel making process go?

The bar stock or blank stock also known as billet blank stock is the first stem in manufacturing. It is the refinement of the raw material into a shape that is useful for further machining processes

What makes a firearm fully automatic?

The firearm will discharge multiple cartridges with a single pull of the trigger

What makes a firearm semi-automatic?

The firearm will discharge one cartridge with a single pull of the trigger

How does the barrel manufacturing technique work?

The marks left behind from tools used during manufacturing of firearm parts allows for the comparison and identification of ammunition components (bullets and cartridge cases)

What is the AFTE Theory of Identification?

Theory of identification as it pertains to the comparison of toolmarks enables opinions of common origin to be made when the unique surface contours of two toolmarks are in "sufficient agreement"

Which of the following is NOT a typical metal used in a bullet jacket?

Titanium

In an impression made by metal injection molded firing pin there may be a line in the middle due to this type of manufacturing process. True or false.

True

The bearing surface of the bullet is where the impressions from the rifling in the barrel are located. True or false.

True

The width of the lands and grooves is a class characteristic for bullets.

True

What does profiling the barrel do?

Turn outside diameter of now rifled bar stock to proper outside dimensions, doing after rifling important because want to have most amount of material present when rifling, rifled bar stock then turned on center, meaning drill hole is now centered within profile of barrel

What does the inconclusive conclusion mean?

Two items can not be identified or eliminated from having been fired by the same firearm due to lack of detail

What does the identification conclusion mean?

Two items were fired by same firearm based on sufficient agreement of individual characteristics

What does the elimination conclusion mean?

Two items were not fired by the same firearm due to a difference in individual and class characteristics

What is a comparison microscope?

Two microscopes connected to an optical bridge which allows viewer to observe two objects simultaneously with same degree of magnification. Can have a monocular or binocular eyepiece

This conclusion is appropriate when the item does not contain markings.

Unsuitable

How does the reaming machining technique work?

Used to smooth out a drill hole and sizing them to the final dimension

How does electrochemical rifling work?

Uses electricity and flow of current to etch into barrel impression of the rifling

How does the end milling machining technique work?

Utilizes a rotating cutter that is perpendicular to the metal work piece. The edges of the cutter have carbide teeth that rip away at the metal. Used to form slots and can be used to face the outside edges of the work piece

How does the milling portion of the breechface manufacturing technique work?

Utilizes rotating cutter that is perpendicular to the metal work piece, breechfaces will have circular or arch marks

How does the broaching portion of the breechface manufacturing process work?

Utilizes series of cutter that start and finish cutting in a single pass. The cutting surfaces are arranged such that each following cutter is slightly larger than the previous, these breechfaces will have series of parallel marks

How does the broaching machining technique work?

Utilizes series of cutter that start and finish cutting in a single pass. The cutting surfaces are arranged such that each following cutter is slightly larger than the previous. Very efficient process and can be used to make a variety of parts

Who was the geologist who developed the optical bridge for the comparison microscope?

Von Inostrazeff

Which one of the following is NOT a breechface mark class characteristic?

Wavy

What is the examination process

When class characteristics are determined, compare items of similar class characteristics, and come to a conclusion

When does firing pin drag occur?

When firing pin is still outside of the aperture when the firearm begins to extract and eject the cartridge

When does firing pin aperture shear occur?

When the primer is scraped along the aperture (hole) for the firing pin in the breechface