Firearms & Toolmarks

1. Firearms & Toolmarks Firearms Identification A discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon. It is not to be confused with ballistics, which is the study of a projectile in motion. Bullet Comparison 1)The barrel of a gun leaves markings on a bullet fired through it that are particular to that barrel. 2)Suspect guns are test fired and the test bullet is compared with the evidence bullet.

2. Firearms & Toolmarks Firearms Identification A gun barrel is produced from A solid bar of steel that has been hollowed out by a drill. Rifling:The spiral grooves formed in the bore of a firearm barrel that impart spin to the projectile when it is fired. Grooves: The cut or low-lying portions between the lands in a rifled barrel Lands: The raised portion between the grooves in a rifle bore.

3. Firearms & Toolmarks • Rifling • The act of making lands and grooves in the barrel of a rifle which impart spin to the projectile fired through the barrel. • Cutting: Prior to 1940 all barrels were machine “cut” by running a steel hook cutter through the barrel which would impart one or two grooves at a time. • 2) Cutting: After 1940 a broach cutter was used so all grooves could be cut simultaneously. • 3) Button Process: A steel plug or “button” impressed with the desired number of grooves is forced under extremely high pressures down the barrel and the inside of the barrel is compressed to form the lands & grooves • 4) Mandrel Rifling: A mandrel rod of hardened steel cut so its form is the reverse of the desired lands & grooves is inserted into a slightly oversized bore. The mandrel-containing bore is then compressed so the lands & grooves are formed.

4. Firearms & Toolmarks As the bullet passes through the barrel, the barrel rifling and other unique characteristics impress markings on the bullet which are unique to that barrel. No two rifled barrels, even those manufactured in succession, have identical striation markings. Striation Markings

5. Firearms & Toolmarks Firearms Identification To compare bullets, an examiner test fires the weapon into a recovery box filled with cotton or a water tank. Bullet Comparison: What to look for 1) Class Characteristics a) The number of lands & grooves b) Their direction of twist. 2) Individual Characteristics a) Striated markings on each bullet b) Done using a Comparison Microscope

6. Firearms & Toolmarks Bullet Comparison Difficulties often arise during the attempt to identify or compare bullets: 1) Grit & Rust in the barrel – can alter the markings on bullets fired through the same barrel 2) Evidence bullet mutilation – commonly, the evidence bullet, when found is mutilated to some degree due to it’s passage through materials (bone, tissue, walls, car doors, etc…) 3) Extended weapon use – as the weapon is fired over & over, the striations on the barrel will change to some degree over time. However, it’s usually not enough to totally eliminate the match 4) Examiner expertise – unlike chemical or instrument analysis, bullet comparison relies on the expertise and experience of the examiner to determine whether two bullets are, in fact, a match.

7. Firearms & Toolmarks An example of bullet mutilation & deformation due to projectile velocity.

8. Firearms & Toolmarks Round-nosed Wad-cutter Semi-wadcutter nyclad Teflon-coat Copper-washed lubaloy THV Solid brassmachined bullet Jacketed soft-point

9. Firearms & Toolmarks Fully jacketed Copper-jacketed Nickel-plated Glaser Safety Slug containing small lead pellets and a plastic plug Federal Expanding Full-Metal-Jacketed (EFMJ) bullet with silicone nose material

10. Firearms & Toolmarks Sabot Round Speer Gold-Dot Jacketed Hollow-point bullet.

11. Firearms & Toolmarks Shotguns have smooth barrels so there is no rifling and no subsequent striations on the projectile. Shotguns are measured by bore size or gauge. 12-gauge – 0.73 in. (1/12th lb) 16-gauge – 0.67 in (1/16th lb) 20-gauge – 0.53 in (1/20th lb) 410-gauge – 0.41 in.

12. Firearms & Toolmarks Cartridge Case Comparison The act of pulling the trigger releases the weapon’s firing pin, causing it to strike the primer, which in turn ignites the gunpowder. The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breechblock (the rear part of a firearm barrel). As the bullet is marked by it’s passage through the barrel, the shell casing or cartridge is marked by contact with the metal surfaces of the weapon’s firing & loading mechanisms.

13. Firearms & Toolmarks Cartridge Case Comparison As with bullets, these markings are distinctive. The shape of the firing pin is impressed into the primer. The breechblock characteristics are impressed into the rear of the cartridge case.

14. Firearms & Toolmarks Cartridge Case Comparison Firing Pin Impressions: these can be very unique and can be seen in both center-fire and rim-fire cartridges.

15. Firearms & Toolmarks Breechblock Cartridge Casing Cartridge Case Comparison Breechmark Comparisons: Here is an example of the markings on the back of the breech being impressed on the casing.

16. Firearms & Toolmarks Cartridge Case Comparison Ejector Marks: These are a function of the ejection mechanism as it grabs the cartridge case and ejects it after firing. Ejector Mechanism Ejector marks 1 Ejector marks 2

17. Firearms & Toolmarks Cartridge Case Comparison Shear Marks: These are made as the cartridge, after being pressed back into the breechblock, is then moved up or down across the firing pin hole and a set of ridges are cut into the casing.

18. Firearms & Toolmarks • Automated Firearms Identification • DRUGFIRE (started by the FBI) and IBIS (started by the ATF) were initially incompatible systems in the early 1990’s. • Around 1998 – 2000 the FBI and ATF joined forces and created NIBIN (National Integrated Ballistics Information Network). • DRUGFIRE focused on examination of spent cartridge casings and stored digital images. IBIS concentrated on expended bullets as well as casings but the two computer storage systems couldn’t be linked (sorta like PC and Mac)

19. Firearms & Toolmarks Configuration of a portion of the IBIS system called “Bulletproof”

20. Firearms & Toolmarks • Gunpowder Residues • Used to help determine the distance from which the weapon was fired. • Distance Determinations: The process of determining the distance between the firearm and a target, usually based on the distribution of powder patterns or the spread of a shot pattern.

21. Firearms & Toolmarks Chemical evaluation of GSR can expand the evidence pattern to include nitrate residue as well as lead and powder residue.

22. Firearms & Toolmarks Following the initial explosion, vaprous lead along with powder, nitrates and other gases are expelled from the barrel

23. Firearms & Toolmarks Tool Marks A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. Most often tool marks are encountered at burglary scenes or other forcible entry scenes. Generally, these marks occur as indented impressions into a softer surface or as abrasion marks caused by the tool cutting or sliding against another object. As with bullets and rifling, here we can have Class Characteristics as well as Individual Characteristics. Class characteristics include the type and shape of tool as well as size. These would be the difference between a screwdriver and a claw hammer or a chisel that was used to force an entry,

24. Firearms & Toolmarks Tool Marks Individual characteristics include random striations generated during the machining of the tool as well as individual edge characteristics like nicks and cuts or ridges and valleys that develop in tools over time. These individual characteristics can be seen in all types of tools from chisels to shovels to cutters and saws.

25. Firearms & Toolmarks Here the casting of a tool mark using silicone brings out the individual characteristics of this prybar. Here both class and individual characteristics can be seen