Firearms

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46 Terms

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  1. Firearms Examination / Identification

is the sub discipline of forensic science where the primary concern is to determine if fired ammunition components (fired bullets, fired cartridge cases, fired shotshells) were fired from a particular firearm.

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 Ballistics 

is sub discipline of forensic science which focuses on the science of the projectile (bullet, shot pellet) to include how the projectile moves while in the firearm, how the projectile moves when it leaves the firearm, and how the projectile affects where it ends. (internal, external, terminal ballistics).

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  1. 1968- The Federal Gun Control Act 

This allowed for better interstate traffic of firearms, mail order sales, etc. Individuals who were convicted of any non-business related felonies, mentally incompetent, and users of illegal substances were not allowed to own or possess a firearm.

THIS LAW ALSO REQUIRED THAT ALL FIREARMS BE SERIALIZED FOR TRACKING PURPOSES!

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  1. 1923- The Frye Standards

Impacted the acceptance of expert testimony. Just when a scientific principle or discovery crosses the line between experimental and demonstratable stages is difficult to combine… while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which particular field it belongs.

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  1. 1969- The Formation of AFTE  

The association of firearm and tool mark examiners. The first official publication of the association, AFTE newsletter number 1 was published 5.15.1969. The name was the AFTE journal.

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1977- The FBI GRC Database 

General rifling characteristics was established in 1977 as part of what was planned to become a multidisciplinary criminalistics lab info system (CLIS). CLIS was discontinued due to the funding, but GRC continued as a standalone project. This is a searchable mainframe computer database of known general rifling characteristics to share as comparison standards of class characteristics of evidence bullets.  From as early as 1950’s.

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1993- The Daubert Standards

required trial judges to be gatekeepers for expert evidence and testimony.

·      Reproducibility of scientific principal

·      Known or potential error rate

·      Existence and maintenance of operating standards

·      Peer review and publication

·      General acceptance in a particular scientific community

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2003- ATF and NIBIN

ATF assumed full responsibility for the NIBIN program. US vs. Odriscoll- the appeal motion to preclude expert testimony was denied. Court ruled that expert testimony in the field of ballistics was relevant and to exclude such evidence would compromise the truth seeking objective of the trial.

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ATF

bureau of Alcohol, Tabacco, and firearms

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NIBIN (national integrated ballistic information network )

1997– created as the agreement between IBIS and DRUGFIRE, expert testimony of the field compromise truth seeking.

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Metal forming techniques

forging, casting, stamping, and machining

gross forming and fine forming

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fine forming techniques

drilling, turning, grinding, milling, broaching

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Rifling of Firearm Barrels 

Spiral grooves are machined on the inner surface of a barrel for the purpose of spin stabilizing the ball or bullet. This determines whether a long arm is a musket or rifle. The firearm component that started modern forensic identification is the rifled barrel.

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Four ways to produce grooves

·      Cut rifling

·      Single point rifling

·      Broached rifling

·      Button swaged rifling

·      Forged rifling

·      Electron discharge machining

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class characteristics

measurable features of a specimen that indicate a restricted group source. Location, size, orientation, relationship of the various parts of a firearm. The manufacturer chooses the class characteristics. They are choosing the design of the gun.

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Individual characteristics

marks produced by the random imperfections or irregularities of tool surfaces. They are unique to a particular tool.

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striated characteristics

occur when there is relative motion between two objects under pressure. Are contour variations on the surface of an object caused by a combination of force and motion, where the motion is approximately parallel to the plane being marked. Could also be described as scratch marks, abrasion marks, or friction marks.

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impressed characteristics

occur when a tool is placed against another object and sufficient force is applied to the tool that an impression is made. The class characteristics can indicate the type of tool used to produce the mark. They can also contain individual characteristics.

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Comparison microscopy

is the most important technique in forensic comparison. It allows simultaneous examination of two separate objects. Convex on both sides and have a short focal length. Compare known and unknown.

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Stereomicroscopy

used for triage. Firing and breech face marks. based on the use of physically joined compound microscopes (one for each eye) in the examination of single objects. 3D view of an object such as a fired bullet being evaluated prior to microscopic comparison with another bullet.

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AFTE theory of ID

  The theory of identification as it pertains to toolmarks enables opinions of common origin to be made when the unique surface contours of two toolmarks are in sufficient agreement.

·      The second of the three principles of the AFTE Theory of identification indicates that the degree of correspondence which must be exceeded to constitute sufficient agreement for an identification is the best known nonmatch (by each individual examiner) to have been produced by different tools.

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Best known nonmatch  

the closest you will get to being the same firearm. consecutive manufacturing

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Range of conclusions 

identification

inconclusive

elimination

unsuitable for comparison

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Identification

 agreement of a combination of individual characteristics and all discernable characteristics where the extent of agreement exceeds that which can occur in the comparison of toolmarks made by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool.

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Inconclusive

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

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Elimination

is a significant disagreement of discernable class characteristics and/or individual characteristics. If a firearm can be shown to have never been subjected to significant use or abuse over a period of time, the qualitative aspects of the striations produced on fired cartridge cases and shotshell cases should remain the same.

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Unsuitable for comparison

this outcome is appropriate for fired and mutilated cartridge cases and shotshell cases that do not bear microscopic marks of value for comparison purposes.

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Challenges for comparisons 

·      Cartridges

·      Inappropriate interchangeability

·      Cartridge cases

·      Reloading toolmarks

·      Manufacture/assembly factors

·      Firearms

·      Use of adaptors

·      Substitution of parts

·      Modifications

·      Manufacturer-related factors

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Case linkage / NIBIN

Files containing fired evidence from unsolved cases. Typically, from shooting incidents which a firearm had not been located or connected to the evidence collected at the scene. Files named, unsolved casefile, open case file, reference fired specimen file, open case ammunition file. Advanced computer-based tools are widely used by laboratories for screening thousands of firearms-related evidence items for potential linkages of incidents. Preliminary can link cases.

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Different ways to recover test fired bullets

water recovery tank and cottonbox

others Wet telephone books, oil or water soaked saw dust, ballistic gelatin, plastic milk jugs, blocks of ice

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water recovery tank

ten feet long and five feet high. Water filled just below the firing port. Firing port is angled to shoot from the top edge to the bottom of the opposite end. Doesn’t damage fired bullet.

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cotton box

usually constructed of wood or

one-eighth to one-quarter inch thick metal plates. The box is

typically, approximately ten feet long and eighteen inches high

and wide, with a hinged lid on the top and a firing port at one

end. The box is filled with cotton waste material that

decelerates bullets fired through the port.

The advantages of this type of bullet recovery apparatus are

that it is

● simple,

● inexpensive,

● easily assembled from readily available materials using in-house agency resources.

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Black powder (components + issues) 

The early mechanical mixture of charcoal, sulfur, and potassium nitrate. Dry components would separate during transportation. Has a limited amount of total energy per unit volume. Volumetrically inefficient- the remaining inert solids, largely dense smoke and fouling, contribute nothing to propulsion. Produces a dense smoke cloud, residue is corrosive to steel.

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Smokeless powder (components + benefits)

Acetone, nitrocellulose, nitroglycerin, and petroleum jelly to form a colloid. (Alfred Nobel) granule control, deterrent coatings, and safe processing had produced ammunition suitable for a wide range or uses.

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Rimfire

the firing pin struck the rim against the rear faces of the barrel, igniting the fulminate. Early rimfire was prone to misfires. Primer is in the rim.

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center fire ammunition

Development focused on placing the pellet of fulminate so that is was better retained. Most design work placed the pellet in the center of the cartridge base.

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single action

The trigger performs one action it releases a cocked hammer

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double action

the trigger performs two actions cocks hammer and release hammer in continuous motion

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Recoil operated

(Hiram Maxim) when parts move less than ½ an inch it is a short recoil (colt model and luger model). When the movement of parts is nearly equal to the length of the cartridge, the term long recoil is applied (Remington model, Browning model). Pulling the trigger should be all that’s required. Recoil energy is redirected to operate the firearm.

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Blowback

directly utilizes the breech pressure exerted on the head of the cartridge to actuate the mechanism. Provides a high rate of fire as a balance for the commonly used less powerful cartridges. Recoil and gas pressure push the bolt open, extract the spent cartridge, cock the firing mechanism, and chamber a fresh cartridge.

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Gas operations

A discharging cartridge produces a large volume of hot gas that can be harnessed to do work. Gas from the barrel is redirected 180 degrees to do work in the direction of the repeating mechanism.

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semi auto

fires one shot each round it automatically ejects the spent case and puts a new one in the chamber

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full auto

will continue to fire rounds as long as the trigger is pulled down. Fires until empty.

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father of firearms

Calvin H. Goddard – made a lot of contributions to firearm and tool mark identification

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gross forming

reduces raw metal stock to a rough form that is intermediate to the required shape.

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fine forming

renders the intermediate form to its final dimensions, with the exception of parts requiring hand fitting.