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CRIMINAL INVESTIGATIONS

CRIMINAL INVESTIGATIONS. AMMUNITION/ BALLISTICS. AMMUNITION. Cartridge Structure Cartridge Case Primer Head Propellant Bullet Blanks- No Bullet. Metal Jacket. Ammunition. AMMUNITION. Cartridge Cases Made of Brass 30% Copper 30% Zinc Aluminum Brass, Plastic and Paper for shotguns.

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CRIMINAL INVESTIGATIONS

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  1. CRIMINAL INVESTIGATIONS AMMUNITION/ BALLISTICS

  2. AMMUNITION • Cartridge Structure • Cartridge Case • Primer • Head • Propellant • Bullet • Blanks- No Bullet

  3. Metal Jacket

  4. Ammunition

  5. AMMUNITION • Cartridge Cases • Made of Brass • 30% Copper • 30% Zinc • Aluminum • Brass, Plastic and Paper for shotguns

  6. AMMUNITION • Function of Cartridge • Expand and seal chamber • Increase Gas Pressure • Press the case up against barrel • Seals • Springs back to almost same size • Aids extraction

  7. AMMUNITION • Shapes • Straight • Bottle neck • Permits more powder • Tapered • Not in use

  8. Ammunition

  9. AMMUNITION • Case Head Designs • Rimmed • Semi-rimmed • Rimless • Rebated • Belted

  10. 5.56 Centerfire vs. Rimfire

  11. AMMUNITION • Caliber Nomenclature • Rifled barrels • Lands and grooves • Diameter of bore from land to land • Sometimes groove to groove diameter • Bullet diameter

  12. Some terminology • Barrel: the metal tube through which the bullet is fired. • Bore: the inside of the barrel, either: Smooth bore: Shotguns. Not smooth bore: rifles, pistols.

  13. Muzzle: the end of the barrel out of which the bullet comes out. • Primer: volatile substance that ignites when struck to detonate the powder in a cartridge.

  14. Types of firearm weapons • Non-rifled: only long • Rifled: short and long

  15. What happens? The holder presses the firing pin which in turn strikes the primer which ignites the powder and produces large amount of hot gas. Produces very high pressure that fires the bullet forcefully through the barrel leaving the muzzle, and onto the target.

  16. Mechanism of injury: • As the missile traverses the body it causes injury by: • Basic contact of bullet and it’s fragments (if present) with the tissue, so larger bullets create bigger damage at the same velocity. • Transferring some of its available kinetic energy to the tissue around it, so increasing velocity greatly increases damage. • It also causes cavitations in the tissue it passes as it accelerates molecules → makes them move centrifugally away from the axis of the bullet.  Bullets do not typically follow a straight line to the target. Rotational forces are in effect that keep the bullet off a straight axis of flight.

  17. SO… • Mode of injury depends on the velocity of the missile -Slow velocity (<340 m/s) speed of sound in air or less -High velocity (1500 m/s) faster! • High velocity missile causes a shockwave around it’s track → severe disruption → ↑tissue pressure and more damage. • So a 10mm wide bullet may cause a 15mm wide track of damage…

  18. Smooth bore weapon (Shotgun): • A gun with a smoothbore that shoots cartridges that contain "shot" or small metal pellets (of lead or steel) as the projectiles. • Ammunition: A shotgun shell(cartridge) may contain one large projectile (called a slug), a few pellets of large shot, or many tiny pellets. Cartridge made of a cylinder fitted into a metal base contains charge of propellant, wads, and shots. • Range is the most important factor, and can be estimated in over half of cases… Close range wounds are severe, but at even relatively short distances, wounding may be minimal.

  19. The rifle weapon: • Rifles differ from shotguns in the length of the barrel and the presence of a butt stock. • They fire one projectile at a time through a thicker barrel that has spiral grooves on its inner surface → rotational movement. • They are much more accurate and shoot more powerful cartridges than handguns. • Ammunition: metal cylinder loaded with explosive propellant and bullet.

  20. Rifle bullet/pistol bullet

  21. AMMUNITION • Caliber Specification • U.S. System not consistent or accurate • .303 Savage = .308 bullet • .303 British = .312 bullet • .30-06 and .308 both fire a .308 bullet • .06 refers to year made

  22. AMMUNITION • U.S. Caliber Designation • Confusing • Not accurate • .38 and .357 • Difference is length of case and grains of powder

  23. AMMUNITION • Black Powder Cartridges • Designated by: • Caliber • Black powder charge • Bullet weight • Examples: • 45-70-405 • Some smokeless powder cartridges used this designation • .30-30

  24. AMMUNITION • Metric Designation • Bullet diameter • Case length • Type of cartridge

  25. AMMUNITION • Types of Cartridge • R = Rimmed • SR = Semi-Rimmed • RB = Rebated • B = Belted • No letter for rimless

  26. AMMUNITION • Additional Terms • Magnum = Higher velocity than standard • Wildcat = Nonstandard, produced by small entity

  27. AMMUNITION • Head Stamps • All cases have stamps on bases • Imprinted for Identification Purposes • Letters • Numbers • Symbols • Trade names

  28. AMMUNITION • Head Stamps (Cont.) • Civilian made with manufacturers symbol • Military made with initials or codes • Year of manufacturing • Match/nm = military match grade ammo • + = NATO • +P or +P+ = High Pressure

  29. AMMUNITION • Bullet Powder Weights • Grain = weight not granules • 1 oz. = 437.5 grains • 1 grain = .0648 grams • Bullet and powder weights measured in grains

  30. AMMUNITION • Primer (Cont.) • Non-corrosive/Non-mercuric • Lead Styphnate • Barium Nitrate • Antimony Sulfide • Most U.S. primers contain all three • *Detection of these compounds provides bases for GSR

  31. AMMUNITION • Primers (Cont.) • Rimfire Ammo • No primer assembly • Primer chemical is in rim

  32. AMMUNITION • Propellants • Black Powder • Charcoal • Sulfur • Potassium Nitrate • Charcoal is fuel • Nitrate supplies oxygen • Sulfur creates density

  33. AMMUNITION • Propellants – Black Powder • When powder burns • Gas = 44% • Residue= 56% • Residue appears as dense white smoke

  34. AMMUNITION • Smokeless Powder • 1884 Vieille – French Chemist • Nitrocellulose • Used EtOH/Ether • Rolled into sheets • Cut into flakes • Single base

  35. AMMUNITION • Smokeless Powder (Cont.) • 1887 – Alfred Noble • Nitrocellulose and Nitroglycerine • Rolled and cut into flakes • Double base

  36. AMMUNITION • Ball Powder Winchester • 1933 • Nitrocellulose dissolved • Formed into balls • Different diameters • Appears uniform round, black spheres or ovals • Reflective surface • Flattened round • Irregular • Flattened chips • Wide variation between round and flat

  37. AMMUNITION • Powder Grains • Disk • Flake • Cylinder • Uncoated (Greenish color) • Coated w/Graphite (shiny black)

  38. Ammunition • Powder (continued) • Powders burn at different rates • Gases and unburned grains are discharged upon firing • Grains can be found in clothing and skin

  39. Ammunition Bullet • Originally lead spheres • Musket vs.. Rifle • Minnie ball (Capt.. Minnie, French Army) • Modern bullets • Lead • Metal-jacketed

  40. Ammunition • Bullets • Various shapes • Round • Hollow point • Semi-wadcutter • Wadcutter

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