Bullet and toolmark analysis
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Ms. Mouser's lecture on Bullet and Toolmark Analysis for Fall 2011 Forensic Science class.
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Bullet and toolmark analysis
- 1. Bullet and Toolmark Analysis
- 2. Bullet and Toolmark Analysis Everything you always wanted to know, but were afraid to ask . . .
- 6. A gun.
- 12. Gun Class Characteristics that you can get off a bullet:
- 16. Enough for a positive ID of a weapon?
- 23. Obstacles to firearms identification
- 24. Obstacles to firearms identification
- 25. Obstacles to firearms identification
- 27. See any rifling?
- 30. Shotgun pellets.
- 31. Shotgun pellets.
- 32. Shotgun slug.
- 33. Shotgun slugs.
- 34. Shotgun firing.
- 35. CODIS, IAFIS . . . meet:
- 36. CODIS, AFIS . . . meet:
- 37. What else Firearms Examiners do
- 38. What else Firearms Examiners do They do more!
- 40. Bang.
- 42. Contact
- 43. Stellate:
- 44. IR light can help visualize GSR on busy fabric:
- 45. Nitrite Residue patterns from known distances.
- 46. Firearms Do’s and Don’ t ’ s
- 47. ___ pick up a firearm by sticking something (like a pencil) into the barrel and then lifting it.
- 48. DON’T pick up a firearm by sticking something (like a pencil) into the barrel and then lifting it.
- 49. ___ pick up a firearm by the checkered grip.
- 50. DO pick up a firearm by the checkered grip.
- 51. ___ unload a firearm before you send it to the lab.
- 52. DO unload a firearm before you send it to the lab.
- 53. ___ record the safety and hammer positions of a suspect weapon before unloading it.
- 54. DO record the safety and hammer positions of a suspect weapon before unloading it.
- 55. ___ mark evidence bullets with your initials on the side of the bullet.
- 56. DON’T mark evidence bullets with your initials on the side of the bullet.
Editor's Notes
- How would you do that? Think Locard’s Exchange.
- How would you do that? Think Locard’s Exchange.
- What parts of the gun do you think leave class or individual characteristics on the cartridges and bullets?
- Answer: The hammer, the inside of the muzzel (or bore), the ejector, and the breechblock
- Together they’re called a cartridge.
- This is the bullet . It’s the actual projectile that comes out the loud end of the gun. This is the casing , or shell . It encloses the whole shebang. This is the powder . This is the stuff that combusts and propels the bullet out of the loud end of the gun. This is the rim . This is what the extractor grabs to eject spent casings. This is the primer . This is what the firing pin hits, which then ignites the gunpowder, which then propels the bullet out of the loud end of the gun.
- You are about to shoot Homer Simpson. Notice the lands and grooves that are about to spin you out of the barrel greatly increasing your accuracy.
- This is what you would look like after you’ve been shot out of the barrel of a gun.
- Caliber of a weapon is measured between opposite lands. Expressed in hundredths of an inch or in mm.
- Caliber of a weapon is measured between opposite lands. Expressed in hundredths of an inch or in mm.
- Caliber of a weapon is measured between opposite lands. Expressed in hundredths of an inch or in mm.
- Caliber of a weapon is measured between opposite lands. Expressed in hundredths of an inch or in mm.
- Striations are the unique pattern of toolmark scratches left on the lands and grooves by the gun manufacturing process. No two guns have the same striations. Striations also change over time as the gun is used. The changes are not so dramatic between firings that positive identifications cannot be made. Just as with fingerprints there is no necessary number of match points for an ID to be made.
- Often your bullets are not in the best shape.
- No examplars for you!
- Mr. Chenney’s “friend.”
- Shotguns have smooth bores.
- What similarity do you see between a shotgun cartridge and a bullet cartridge?
- Shotgun cartridges are packages of “shot” or lots of bb’s. Shotguns come in gauges, not caliber.
- This is shot.
- Shot comes in different sizes.
- If a shotgun cartridge contains only a single shot, it’s called a slug. This is a slug. Ouch.
- Slugs also come in lots of different sizes.
- Here’s what a shotgun cartridge looks like as it leaves the barrel. The spread of shotgun pellets expands approximately 1 inch for every yard travelled from the barrel.
- Since 1999: NIBIN obtained over 2 million records NIBIN partners have confirmed more than 40,000 NIBIN hits (matches) NYPD has become the most successful user of NIBIN with 2,500 plus hits
- Since 1999: NIBIN obtained over 2 million records NIBIN partners have confirmed more than 40,000 NIBIN hits (matches) NYPD has become the most successful user of NIBIN with 2,500 plus hits
- When a gun goes off, a lot more leaves the barrel than just the bullet.
- You can look at the pattern of the gunshot residue on the target to make a guess about the distance of the shooter from the target.
- Characteristics: A hole Visible ring around the hole, aka bullet wipe Burned or singed material around the bullet hole Sometimes the hole is accompanied by a stellate, or star shaped tear pattern
- This will damage the striations on the inside of the barrel or dislodge dirt and material that may have contributed to individual characteristics on your evidence bullets.
- Go for it! The bumpy part of a gun handle doesn’t take prints well. You won’t be disturbing any usable latents by handling the gun there.
- Uh, yes, please! I think the lab technicians will appreciate if you don’t send them loaded ammo in the mail.
- Yup. You need to make sure the gun is safe before you collect it as evidence, but you should also record everything about the gun that you can before you send it off.
- Nope. Mark the bullet either on the nose or the base to avoid damaging those precious striations again.