Name_____________________________________________________________________Date___________________________Period_______
Unit 16 Test Review
1.
What are the 2 main categories of firearms? How do they differ?
Technically, 1. handguns (pistols and revolvers held in hand with shorter barrels) and
2. long guns (rifles and shotguns held with two hands that have
long barrels). Handguns and rifles are rifled having barrels with
lands and grooves; whereas, shotguns do not. They have barrels
that are smooth. Shotguns fire shells packed with small lead
balls. Rifles and handguns fire casings having a single lead
projectile (bullet) inside.
2.
What are 2 examples of rifled firearms? What is an example of a smooth barrel firearm?
1. Handguns and
2. Rifles. Shotguns have smooth barrels.
3.
spiral grooves are etched or cut into the bore of a firearm barrel that spin
the projectile when it is fired, forming a right or left twist.
4.
What are lands and grooves? What is the purpose of rifling? Label the diagram.
Define rifling:
Lands are the raised portions between the grooves in a rifled bore; Grooves are the
cut or low-lying portions between the lands in a rifled bore. Rifling makes the bullet
travel longer distances and more accurately toward the target.
5.
What are the 3 different types of methods used to create rifling in a firearm? Describe each.
1. Button – forces grooves into the metal under high pressure as the barrel surround
the button.
2. Broach – a set of steel rings on a rod that cuts the grooves into the barrel as the rod
is rotated down the length of the barrel.
3. Mandrel – a rod the same length as the barrel and has a reverse rifling pattern on
the outside. It is placed inside an oversized barrel and the rifling is rolled or hammered
into the inside of the barrel.
6.
What is caliber? What category of firearm is measured in caliber? How is caliber measured?
Rifles and handguns are all measured in caliber which is the system used to determine
the bore diameter of those firearms. Caliber (bore diameter) is measured from a land
on one side of the bore to a land on the direct opposite side of the bore, usually in
“mm” (i.e. 9mm caliber) or hundredths of an inch (0.22 inch caliber).
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7.
What is gauge? What category of firearm is measured in gauge? How is gauge measured?
Only shotguns are measured in gauge, the system used to measure their smooth bore
diameter or “shotgun size”. Originally it was measured as the number of lead balls
with the same diameter as the barrel that would make a pound of lead (i.e. 16 gauge
shotgun has a bore diameter equal to the ball diameter of 16 equally sized lead balls
made from one pound of lead).
8.
Which shotgun has the smallest barrel diameter….12 gauge or 16 gauge? Why?
Answer: 16 gauge will have the smaller bore (barrel) diameter. The rule is: the higher
the gauge #, the smaller bore diameter.
9.
What happens when a handgun or rifle is fired? List all the steps in order.
1. Trigger is pulled.
2. Firing pin strikes back of primer cup (leaving an impressed mark) located at bottom
of cartridge case causing primary explosive to ignite.
3. Primary cup explosion causes gunpowder in the rest of the cartridge case to
explode.
4. Burning gunpowder causes chemical reaction producing large amounts of gases.
5. Produced gases fill space in cartridge case until no more room, causing the bullet to
be forcefully separated from case. Bullet is forced down the barrel spinning, leaving
land and groove marks impressed on its sides.
6. Meanwhile, the cartridge case is forcefully pushed back against the breechface
(rear wall of firing chamber) leaving impressed marks on the bottom of case.
7. Extractor leaves an impression mark on the rim of the case as it removes it from
the firing chamber.
8. Finally, ejector leaves an impression on the case as it forcefully ejects or removes it
from the firearm altogether.
10.What is the extractor? Does this produce any markings that can be used as evidence? Explain.
Extractor is a mechanism near the firing chamber that leaves an impression mark on
the rim of the case as it removes it from the firing chamber. The mark left on the rim is
considered individualistic evidence and can be traced back to an individual weapon to
the exclusion of all others.
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11.What is the ejector? Does this produce any markings that can be used as evidence? Explain.
Ejector is a mechanism near the firing chamber that leaves an impression mark on the
case as it forcefully ejects or removes it from the firearm altogether. This mark left on
the sides of the case is also considered individualistic evidence and can be traced back
to an individual weapon to the exclusion of all others.
12.Why must a suspect’s hands be swabbed immediately for gunpowder residue?
What areas of the hand are
generally swabbed for GSR?
The suspect could easily remove the GSR by hand-washing, putting hands in pockets,
or wiping hands off onto another garment. Three areas are swabbed: 1. Thumb web
area, 2. Back of hand, 3. Palm of hand.
Lead core
13.On the diagram above, label the parts of the ammunition. Which category of firearm uses this type of
ammunition? Rifled firearms (handguns and rifles).
14.Referring to the diagram above, which parts of the ammunition will show individual characteristics?
Primer cup (firing pin impression), Extractor groove, Case (ejector impression), Copper
jacket (striations within the lands and grooves), and bottom of case can have
impressed marks from being pushed backward and hitting the breechblock (rear part
of firing chamber).
15.How does the ammunition for rifles and handguns differ from that used in shotguns? What are the parts of the
shotgun shell? Ammunition for rifles and handguns does not have a “wad” or “packing”
inside the case and does not have numerous small pellets called shot as the
projectile… shotguns do have these. The plastic shotgun shell has a primer cup,
gunpowder, wad or packing, and then numerous small lead balls as the projectile.
Shotgun shells can sometimes have a single, solid,
lead, “slug” projectile instead of the small lead balls.
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16.Describe how examiners could determine that a gun had been fired less than 1 inch from the victim. A starshaped (stellate) tear pattern around the bullet hole entrance and a rim of smokeless
deposit of vaporous lead around entrance.
17.Describe how examiners could determine that a gun had been fired from a distance of approximately 12 to 18
inches from the victim. No stellate tear pattern but the presence of a halo or circle of
smokeless deposit of vaporous lead out from the bullet entrance.
18.Describe how examiners could determine that a gun had been fired from about 25 inches to up to 36 inches
from the victim. No stellate tear pattern but the presence of scattered specks of burned
and partially burned powder grains without any halo of soot as in 12-18”.
19.Forensic investigators determined from the victims clothing that the shooter was at least 3 feet away. How
would they have come to this conclusion? A dark ring around the hole entrance (“bullet wipe”)
and no presence at all of powder residue.
20.What are the proper techniques for collecting discharged bullets and cartridges at the crime scene? Bullets
are marked with investigator’s initials on the base or nose and then wrapped in tissue
paper and placed in small rigid container. Cartridge casings are marked with initials
near the outside mouth and then wrapped in tissue paper and placed in small rigid
container. Discharged shotgun shells are initialed on the plastic tube or on the metal
nearest the mouth of the shell.
21.What are the proper techniques for collecting firearms at the crime scene? Can be held by the edge of
the trigger guard or the textured grip. All ammunition should be unloaded from
weapon and position recorded if removed from a revolver. Weapon can be marked
using a tag on the trigger guard and then packaged in a cardboard box.
22.What is NIBIN? What is IBIS? What are the 2 components of IBIS? NIBIN (National Integration
Ballistics Information Network) is a database of surface characteristics on evidence
bullets and cartridge casings, as well as test fires from suspect weapons. IBIS
(Integrated Ballistics Identification System) uses Brasscatcher to compare cartridge
cases and Bulletfire to compare bullets.
23.How are serial numbers restored when they have been obliterated? How does this process work? When a
serial number is stamped or impressed into metal, the metal crystals are permanently
strained in positions corresponding to the location of the numbers. This stamped zone
extends a short distance beneath the original impressed numbers. The metal surface
is grinded down to remove visible numbers, but an acid etching solution added to the
metal surface will dissolve the metal in the stamped zone faster than the surrounding
area causing the numbers to appear again.
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24.What are the proper techniques for collecting tools and tool marks at the scene of a burglary? All evidence
marks and suspect tools should be thoroughly photographed with a scale. Suspect
tools should never be packaged with the evidence tool marks to prevent contact that
could alter the evidence. If possible, the entire object bearing the tool mark should be
submitted to lab.
25.What are considered class characteristics for tool marks? Individual characteristics? Class = size and
shape of tool. Individual = presence of minute imperfections on a tool that are part of
the tool’s impression.
26.What tool is most commonly used for comparison of firearms and tool marks? Comparison Microscope
is used to compare tool marks found at the crime scene with test mark impressions
made from the suspect tools.
27.How are objects bearing tool marks usually submitted to the crime lab? When possible, the entire
object or the part of the object bearing the tool mark should be submitted to the lab.
Never attempt to fit the suspected tool into the tool mark.
28.
A victim was found lying in the park on the ground 500. ft. from a building along the horizontal. A muzzle flash
was witnessed coming from the 10th story of the same building. Each story is 10. feet. What angle did the bullet
hit the victim in the head while sunbathing on the grass? How far away did the bullet travel from muzzle to
wound?
Bullet traveled ~510 ft from muzzle to wound = hypotenuse
Bullet hit victim at ~11 degree angle of impact.
(see work below on pg. 6)
29.Solving the above equation:
Tangent of angle of impact TOA
You would use the opposite and hypotenuse with what? Sine of angle of impact SOH
You would use the hypotenuse and adjacent sides with what? Cosine of angle of impact CAH
a. You would use the adjacent and opposite sides with what?
b.
c.
30.What forces act on a bullet? What are the 2 components? Forward force of gunshot and
downward force of gravity. The forward force is the horizontal component and the
downward force is the vertical component.
31.
A shooter with a rifle is located in a tree. The tree is located 600.m away from the victim along the horizontal.
It takes the bullet 1.1s to hit the victim at an angle of 25. degrees in the left side 0.75m up as he sits on a park
bench.
a.
How high up was the shooter?
~280m
b. What was the speed of the bullet at impact?
~590 m/s
(see work on pg. 7)
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= sin-1 (0.19607)
= 11.36487 ~ 11 deg
= cos-1 (0.980392)
= 11.36487 ~ 11 deg
= tan-1 (0.2)
= 11.36487 ~ 11 deg
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