Please enable JavaScript.
Coggle requires JavaScript to display documents.
Firearms Examiner Training. Dillon JH, Jr. 2013. Firearms Examiner…
Firearms Examiner Training. Dillon JH, Jr. 2013. Firearms Examiner Training. [Accessed 26 March 2020] from
https://firearms-examiner.training.nij.gov/module10/
Module 10: Characterization and Evaluation of Fired Projectiles
I. Recovered Bullets and Projectiles
A. Report
Descriptive information (e.g., caliber, construction, possible cartridge types, and possible manufacturer)
General rifling characteristics
Listing of possible firearms that may have produced the general rifling characteristics
Evidentiary potential based on individual characteristics present
B. Examination
Preliminary steps
a. Review laboratory protocols, as needed
b. Complete administrative requirements
c. Chain of custody
d. Marking of evidence
e. Laboratory case identifiers
f. Investigative file identifier
g. Examiner identity
h. Quality assurance
i. Follow laboratory safety protocols
j. Determine the presence of trace evidence and follow laboratory protocol for collection
i. Examples
• Paint
• Glass
• Blood
• Bone
• Soft tissue
• Hair
• Fibers
• Wood
• Metal smears
• Masonry
• Stone
k. Determine if latent fingerprint examinations should be performed prior to toolmark examinations
l. Determine if other examinations (not requested) should be performed. If so, coordinate with the investigator.
Observations and determinations
a. Bullet weight
b. Composition of the bullet
c. Base description
d. Type and position of cannelures
e. Manufacturer/marketer
f. General rifling characteristics
i. Caliber
ii. Number of land and groove impressions
iii. Direction of twist
iv. Width of the land and groove impressions
g. Bullet design
h. Extraneous marks due to firing (skid marks/slippage, shave marks, flared base)
i. Suitability for comparison purposes
Conclusions
a. A description of the fired bullet in terms of its caliber, construction, and the cartridge types possibly represented and its manufacturer
b. The general rifling characteristics observed
c. A list of the brands and types of firearms that could have produced the general rifling characteristics observed in its surface
d. The evidentiary potential of the fired bullet in terms of whether or not it bears sufficient microscopic marks for later comparison if a suspect firearm is recovered
C. Physical Features
Modern bullets
a. Plain lead bullets (swaged or cast)
b. Jacketed bullets (heavy core enclosed by an outer jacket or gliding metal)
Terminology
a. Bullet
i. Non-spherical projectile for use in a rifled gun barrel
b. Tip
i. Extreme forward end of a bullet
c. Meplat
i. Blunt tip of some bullets, specifically the diameter of that blunt tip
d. Ogive
i. Curved forward part of a bullet
e. Nose
i. Forward end of a bullet, including the tip, the ogive, and meplat (if present)
f. Cannelure
i. Circumferential groove in a bullet generally of a knurled or plain appearance for the purpose of lubrication or identification, or to assist in crimping a bullet in the mouth of a cartridge case
g. Bearing surface
i. Portion of the outer surface of a bullet that makes direct contact with the interior surface of a gun barrel
h. Base
i. Rear portion of a bullet
i. Heel
i. Configuration of the intersection of the bearing surface and base of a bullet
Characteristics
a. Primary physical features of bullets
i. Weight
• Considerations
– Laboratory safety protocols should be followed.
– Laboratory trace evidence policies should be followed prior to and during removal of any material adhering to a bullet.
– Bullets should be cleaned so as to not damage the surfaces potentially bearing microscopic marks.
∆ Soak in a mild detergent to loosen any adhering material. Gently scrub using a soft bristled toothbrush.
∆ Use an ultrasonic cleaner and appropriate fluid.
3 more items...
∆ Use appropriate tools to mechanically remove debris (e.g., embedded wood particles, bone, cartilage).
– Weigh each bullet fragment separately because they may or may not originate from a single bullet. Individually weighed fragments can be regrouped later, if necessary.
ii. Measured caliber/diameter
• The measurement should be taken at an alternate location
– Significant base mutilation upon impact, altering the width or apparent caliber
– Unusual amount of base expansion after firing (e.g., deep hollow-based lead bullets)
– Unusual base expansion of lead bullets after firing from a short-barreled handgun
iii. Composition
• Basic types of compositions
– Solid bullets
∆ Swaged and cast land
∆ Single metal (e.g., steel, aluminum, zinc, copper alloys, and brass)
– Bullet jackets
∆ Jacketing metals (e.g., copper alloys, brass, aluminum, nickel, and steel)
– Bullet cores
∆ Heavier metals (e.g., lead and steel)
– Bullet coatings
∆ Coasted/washed/plated copper, brass, nylon (Nyclad), Teflon
– Sabots
∆ Plastic sleeve or adaptor surrounding a sub-caliber bullet that allows it to be fired in a larger caliber firearm. The projectile never directly touches the barrel, and the sabot typically falls away after firing. Because the bullet never directly engages the barrel, rifling impressions will not be impressed on the bullet but rather the sabot.
iv. Jacket type
• May be fabricated in a number of configurations
– Full metal jacket - encloses the entire bullet, except for the base. Normally used for military purposes, these bullets are also known as full jacketed, full patch, full metal case, and ball ammunition.
– Semi-jacketed partially encloses the bullet with the exception of an exposed soft point or a hollow point.
– Total metal jacket fully encloses a bullet core.
v. Magnetic properties
• Damaged, mutilated, and deformed bullets may not yield accurate measurements.
vi. Length
• Damaged, mutilated, and deformed bullets may not yield accurate measurements.
vii. Color/finish
• Examples
– Armor-piercing bullets are designed to pierce metal. They usually contain a hardened core or are completely composed of a substance other than lead or lead alloy.
– Exploding bullets contain a primer or other explosive and are designed to explode upon impact.
– Frangible bullets are designed to disintegrate upon impact with a hard surface in order to minimize ricochet.
– Incendiary bullets contain a chemical compound that ignites upon impact, starting a fire.
– Tracer bullets contain a burning compound in the base to permit observation of bullet flight.
viii. Base construction
• Examples
– Solid base bullet composed of one material with no jacketing
– Open base - jacketed bullet with the core exposed
– Jacketed solid base - jacketed bullet with the core enclosed
– Gas check bullet - composed of a lead bullet with a shallow copper alloy cup fitted to the base
ix. Base shape
• Common variations
– Flat base
– Stepped recess
– Concave recess
– Parabolic concave recess
– Conical recess
– Truncated conical recess
– Concave recess with convex protrusion in the center
– Convex base
– Conical convex base
– Parabolic convex base
– Truncated base bullet
x. Nose construction
• Examples
– Soft point bullets provide for exposure of a portion of the core at the nose of a jacketed bullet.
– Jacketed hollow point bullets have a cavity in the nose to facilitate expansion.
– Semi-jacketed hollow point bullets have an exposed portion of the lead nose that contains a cavity.
– Metal point bullets (capped bullets) consist of a standard lead bullet with a harder metal jacket over the nose to enhance bullet penetration.
– Solid nose constructed of a single metal or alloy.
xi. Nose shape
• Configurations
– Round nose bullets are elongated with a nose measuring half that of the bullet diameter (half of the bullet diameter).
– Pointed types
∆ Spitzer bullets have a sharp point and a long ogive.
∆ Conical bullets/conoidal bullets have a cone shape.
– Wadcutter bullets have a sharp shouldered nose intended to cut target paper cleanly to facilitate accurate scoring.
– Flat nosed bullets have a flattened tip at right angles to its axis.
– Semiwadcutter bullets have a distinct short truncated cone at the nose end.
– Truncated bullets are conical with a flat nose.
xii. Cannelures
• Two types
– Knurled
– Smooth
D. Manufacturer Determination
Standard Ammunition File Sources
a. Materials may be obtained from
i. Individual boxes of ammunition purchased for use in casework
ii. Seized ammunition in original boxes
iii. Evidence ammunition being disposed of by evidence custodians of the courts
iv. Training and operational ammunition obtained from enforcement agencies
b. Identification Resources
i. Line drawings and dimensional data of industry ammunition specifications available through Sporting Arms and Ammunition Manufacturers Institute, Incorporated
ii. Manufacturers brochures, catalogs, and websites
E. General Rifling Characteristics
Categories
a. Caliber (bore diameter)
b. Number of land and groove impressions
c. Direction of twist
d. Land and groove impression dimensions
i. Techniques
• Examiners notes should reflect
– measurements expressed to the nearest thousandth of an inch
– measurements of useable land and groove impressions
– number of measurable land and groove impressions
– number of visible land and groove impressions
ii. Equipment
• Micrometer
• Calipers
• Glass measuring reticule
– Bring both reference points into focus
– Place the bullet on a fixed mount that can be rotated.
– Rotate the bullet to the selected land or groove impression.
– Superimpose the measuring grid of the eyepiece on the surface of the bullet.
– Take a measurement reading to the nearest thousandth of an inch.
– Rotate the bullet to the next land or groove impression and repeat steps 3-5.
• Electronic reticule
– Place the bullet on a fixed mount that can be rotated.
– Rotate the bullet to the selected land or groove impression.
– Bring both reference points into focus
– Superimpose the measuring grid of the eyepiece on the surface of the bullet.
– Take a measurement reading to the nearest thousandth of an inch.
– Rotate the bullet to the next land or groove impression and repeat steps 3-5.
• MP 6 optical projector (no microscope)
– Mount the nose of a bullet on a moveable stage - the bullet image is projected onto a hooded screen that displays a measuring grid.
– Bring both edges of the selected land or groove impression into focus.
– Align one reference point on the impression with a line on the measuring grid - the reference point is designated as zero.
– Move the bullet and its mount by rotating the knob until the next reference point is reached the width of the land or groove impression is displayed in an LED readout in thousandths of an inch.
– Rotate the bullet on its mount to the next land or groove impression.
– Repeat steps 2-5 until all land and groove impressions are measured.
• Machinists scale
• Digital measuring equipment and software
iii. Comparison Microscope
• Place a fired evidence bullet on a bullet mount on one stage of the comparison microscope.
• Mount the micrometer, jaws up, on the other stage.
• Set the objective lenses for both stages to the same magnification.
• Focus both lenses.
• Open the jaws of the micrometer to match the reference points on the fired bullet.
• Record reading (air gap) to the nearest thousandth of an inch.
• Rotate the bullet to the next land or groove impression.
• Repeat steps 4 - 7 until all land and groove impressions are measured.
iv. Stereomicroscope
• Place a fired evidence bullet and the micrometer under the microscope.
• Open the jaws of the micrometer to match the reference points on the fired bullet.
• Record the reading to the nearest thousandth of an inch.
• Rotate the bullet to the next land or groove impression.
• Repeat steps 2 - 4 until all land and groove impressions are measured.
Measuring Impressions
a. Considerations
i. The widths of the land and groove impressions are small and must be accurately measured.
ii. A discipline-wide technique must be used to ensure reproducibility of results to compare against a standard.
F. FBI GRC File Standards
input data for searching the GRC file
a. Caliper
b. Number of lands and grooves
c. Direction of twist
d. Land and groove impression measurements
e. Other information
II. Damaged Bullets
A. There may be retrievable information if all of the following are present
One or more measurable land impression
One or more measurable groove impression
Sufficient bullet remains to determine a measured caliber
B. Microscopic Marks
Goes beyond class characteristics by being
a. Unique to a particular firearm
b. Reproducible shot after shot
c. Identifiable with a specific firearm
Possibilities
a. Microscopic marks are
present and sufficient
for comparison purposes
b. Microscopic marks are
present, but insufficient
for comparison purposes
c. Microscopic marks are
not present
, precluding an identification
Bullet Design
a. Impact the ability to find and evaluate microscopic marks
i. Coated bullets are lead alloy bullets with a thin coating of another substance (not a jacket).
• Nyclad is an inert nylon coating. While this type of bullet will have impressions on the bearing surface after firing, they are typically less well defined and more difficult to measure.
• Copper or brass plated/washed bullets are covered with a thin alloy coating that can make reading dimensions more difficult because of their propensity for peeling.
• Teflon coated bullets retain very little microscopic detail of value for comparison purposes.
ii. Exploding bullets contain a primer or explosive and are designed to explode upon impact, resulting in an unreadable bearing surface.
iii. Frangible bullets are designed to disintegrate upon impact with a hard surface to minimize ricochet. No measurable bearing surface remains.
iv. Sabots are lightweight collars that allow smaller, lighter bullets to be fired. Microscopic marks are found on the sabot but not on the bullet.
Effects of Firing
a. Some effects of firing that are of value to the firearm examiner
i. Shaving (shearing) is the cutting of metal from the surface of a bullet due to cylinder misalignment in a revolver. A large amount of shaving may leave a void in the bearing surface of a bullet, which may not receive rifling impressions.
ii. Skid marks ( slippage ) form on the bearing surface of bullets as they enter the rifling of the barrel before the bullet engages the rifling. Skid marks are typically produced by revolvers and have the appearance of widening the land impressions at the nose of the bullet. Taking measurements in this area should be avoided; base measurements are more accurate.
iii. Flared bases of bullets fired from short-barreled handguns or bullets with deep base cavities are subject to expansion after leaving the barrel of a firearm. Measuring a flared base would be misleading; the better-protected base normally provides the best dimensional data.
iv. Blowby is the escaping of gases past a fired bullet while the bullet is still in the barrel. These high-pressure gases are at a very high temperature and can melt or etch the bearing surface of plain lead bullets. As a result, the width of rifling impressions can be seriously degraded and appear very blurry and indistinct.
v. Barrel leading ( metal fouling) is the accumulation of lead or bullet jacket material in the bore of a firearm due to the passage of bullets. This condition may preclude obtaining reliable land and groove dimensions.
vi. Corroded/rusted barrels occur due to poor care and maintenance and affect bullet bearing surfaces in the same way as metal fouling or leading.
vii. Lead smears may be deposited on the surface of bullet jackets, obscuring the edges of the land and groove impressions.
b. They can be removed by
i. 10cc of glacial acetic acid
ii. 2cc of 30% hydrogen peroxide
iii. 70cc of distilled or DI water
C. Impact Damage
Extreme damage
a. The bullets are processed as follows
i. Trace evidence of value is recovered
ii. All debris is removed
iii. Rifling impressions in undamaged areas are evaluated
Mushrooming
a. The controlled expansion is advantageous to police operations in
i. Minimizing the danger to innocent bystanders
ii. Ensuring the delivery of all bullet energy to the intended target
D. Fired Shotshells Components
May be comprised ofa number of components
a. Card (paper) or fiber disks
b. Plastic wadding components
c. Lead, steel, bismuth, or tungsten alloy shot pellets
d. Shotgun slugs
e. Shot buffer materials (granular plastic particulate)
Wadding Material
a. The examiner may be able to determine
i. The gauge of the shotgun
ii. The manufacturer or marketer
iii. A range of possible shot sizes based on impressions in the wad
iv. Individual characteristics (in some cases)
b. They may include
i. Card wad
ii. Shot collar
iii. Over-shot wad or top wad
iv. Under-shot wad
v. Filler wad
vi. Over-powder wad
vii. Cup wad
c. Several difficulties
i. Tend to absorb body fluids
ii. Swell beyond their original dimensions
iii. Often dry without retaining original dimensions
iv. Are more easily damaged than plastic wadding materials
d. Types of plastic wadding materials include
i. Shot protector wad
ii. Shot collar
iii. Combination wad
Shotshell Projectiles
a. shot pellets determination of size, composition, and other physical characteristics
b. buckshot determination of size
c. shotgun slugs determination of manufacturer or marketer, gauge, and individual characteristics (in some cases)
E. Examination
Laboratory policies
a. Chain of custody
b. Laboratory safety
c. Trace evidence
i. Coordination of examination sequencing across disciplines to preclude loss of trace evidence.
Preliminary Procedure
a. Mark evidence according to laboratory procedures
i. Shot pellets, buckshot, and buffering materials by nature are impractical to mark directly. Their packaging should be marked and appropriate notations made in the related worksheet.
b. Photograph and document original condition of evidence
c. Determine equipment necessary for examination
i. Laboratory-approved worksheet
ii. Reference standards
iii. Stereomicroscope
iv. Evidence marking items
v. Small hand tools, as required
vi. Equipment for measuring dimensions of components, such as
• Calipers
• Stereomicroscope with micrometer and calipers
• Stereomicroscope with optical grid
• Stereomicroscope and machinists steel rule
• Measuring projector
• Comparison microscope with micrometer (air gap method)
Wadding Material
a. The steps for this procedure are as follows
i. Perform preliminary procedures
ii. Compare all physical characteristics of the evidence wadding component to the standards of similar manufacture and composition, including these:
• Color
• Dimensions
– Measure diameter; use to determine gauge
– Measure length
• Design (number of petals, composition, shape)
– Determine composition
– Determine number of petals plastic wads only
– Describe shape
• Shot size
– Determine range of shot sizes as indicated by impressions on wadding material.
iii. Disassemble one unfired evidence shotshell for physical comparison of wadding materials, if required and available.
iv. Acquire fired standards for comparison, if wadding is deformed and distorted.
v. Identify individual markings (these are unusual when found).
• Compare striated marks (if present) on wadding materials with standards fired from the evidence firearm.
Shot Pellets
a. The steps for this procedure are as follows
i. Perform preliminary procedures
ii. Record the total number of pellets received
iii. Determine the composition of the pellets received
iv. Determine the total number of pellets suitable for weighing
• Note whether or not all of the pellets appear to be similar. If not, group them accordingly.
v. For each type of pellet present, weigh pellets together for total weight in grains or grams.
vi. Divide the total weight of pellets by the total number weighed to obtain an average pellet weight.
vii. Determine the shot size based on the average pellet weight of the evidence shot by comparing to a standard table of shot sizes.
viii. The weight of evidence pellets can also be directly compared to the weight of standards using the same number of pellets until a similar known weight is obtained.
Dimension
a. The steps are as follows
i. Perform preliminary procedures
ii. Determine the total number of pellets received
iii. Determine the composition of the pellets
iv. It may be useful in some cases to enlist the aid of an instrumental chemist in determining the composition of non-lead shot.
v. Determine which pellets are suitable for measuring. For example, determine which pellets roll freely; pellets that roll freely should be measured.
vi. Measure and record the diameters of the pellets in hundredths or thousandths of an inch. For small pellets, it is generally appropriate to record three decimal places; for buckshot, two decimal places are appropriate.
vii. Determine the shot size of the evidence shot by comparing to a standard table of shot sizes. Note that industry sources indicate shot designated as a certain size may vary up to plus or minus half a shot size.
Shotgun Slugs
a. The steps are as follows
i. Perform preliminary procedure
ii. Record the observable physical characteristics
• Dimensions
– Measure diameter; use to determine gauge
– Measure length
• Measure weight
• Design
– Determine composition
– Describe shape (base, nose, etc.)
– Describe slug rifling
iii. Compare physical characteristics with laboratory standards or other evidence items.
iv. Identify individual markings (these are unusual when found).
• Compare striated marks (if present) with standards fired from the evidence firearm.
Buffer Material
a. Shot buffer materials may be shown to be consistent with laboratory standards or other evidence items through the following procedure:
i. Perform preliminary procedures
ii. Compare all physical characteristics of the evidence buffer materials to the standards of similar manufacture and composition, including
• Color
• Shape
• It may be useful in some cases to enlist the aid of an instrumental chemist in determining the composition of buffer materials
iii. Examine questioned surface(s) visually and microscopically for the presence of buffer materials.