Name Date Period. Unit 16 Test Review

Transcription

1 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. Define rifling: 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. 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). 1

2 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. 2

3 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. 3

4 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 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. 4

5 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 10 th 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: a. You would use the adjacent and opposite sides with what? Tangent of angle of impact TOA b. You would use the opposite and hypotenuse with what? Sine of angle of impact SOH c. You would use the hypotenuse and adjacent sides with what? Cosine of angle of impact CAH 30. What forces act on a bullet? What are the 2 components? Forward force of gunshot and downward force of gravity. 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) The forward force is the horizontal component and the downward force is the vertical component. 5

6 = sin-1 ( ) = ~ 11 deg = cos-1 ( ) = ~ 11 deg = tan-1 (0.2) = ~ 11 deg 6

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