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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 AMMUNITION/ BALLISTICS
AMMUNITION • Cartridge Structure • Cartridge Case • Primer • Head • Propellant • Bullet • Blanks- No Bullet
AMMUNITION • Cartridge Cases • Made of Brass • 30% Copper • 30% Zinc • Aluminum • Brass, Plastic and Paper for shotguns
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
AMMUNITION • Shapes • Straight • Bottle neck • Permits more powder • Tapered • Not in use
AMMUNITION • Case Head Designs • Rimmed • Semi-rimmed • Rimless • Rebated • Belted
Rimmed • Rimmed cartridges use the rim to hold the cartridge in the chamber of the firearm, with the rim serving to hold the cartridge at the proper depth in the chamber this function is called “headspacing”
Semi-Rimmed • On a semi-rimmed case the rim projects slightly beyond the base of the case, though not as much as a rimmed cartridge.
Rimless • On a rimless case, the rim is the same diameter as the base of the case • It is known as an extractor groove. Since there is no rim projecting past the edge of the case
Rebated • Rebated rim cartridges have a rim that is significantly smaller in diameter than the base of the case, serving only for extraction. • Functionally the same as a rimless case, the rebated rim provides some additional benefits when considered in conjunction with other cartridges.
Belted • The purpose of the "belt" on belted cases is to provide headspacing. • The extractor groove is cut into the belt just as it is cut into the case head on a rimless case. • The belt as as a rim on what is essentially a rimless case
AMMUNITION • Caliber Nomenclature • Rifled barrels • Lands and grooves • Diameter of bore from land to land • Sometimes groove to groove diameter • Bullet diameter
AMMUNITION • Types of Cartridge • R = Rimmed • SR = Semi-Rimmed • RB = Rebated • B = Belted • No letter for rimless
AMMUNITION • Additional Terms • Magnum = Higher velocity than standard • Wildcat = Nonstandard, produced by small entity
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
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
AMMUNITION • U.S. Caliber Designation • Confusing • Not accurate • .38 and .357 • Difference is length of case and grains of powder
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
AMMUNITION • Metric Designation • Bullet diameter • Case length • Type of cartridge
AMMUNITION • Head Stamps • All cases have stamps on bases • Imprinted for Identification Purposes • Letters • Numbers • Symbols • Trade names
AMMUNITION • Bullet Powder Weights • Grain = weight not granules • 1 oz. = 437.5 grains • 1 grain = .0648 grams • Bullet and powder weights measured in grains
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
AMMUNITION • Primers (Cont.) • Rimfire Ammo • No primer assembly • Primer chemical is in rim
AMMUNITION • Propellants • Black Powder • Charcoal • Sulfur • Potassium Nitrate • Charcoal is fuel • Nitrate supplies oxygen • Sulfur creates density
AMMUNITION • Propellants – Black Powder • When powder burns • Gas = 44% • Residue= 56% • Residue appears as dense white smoke
AMMUNITION • Smokeless Powder • 1884 Vieille – French Chemist • Nitrocellulose • Used EtOH/Ether • Rolled into sheets • Cut into flakes • Single base
AMMUNITION • Smokeless Powder (Cont.) • 1887 – Alfred Noble • Nitrocellulose and Nitroglycerine • Rolled and cut into flakes • Double base
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
AMMUNITION • Powder Grains • Disk • Flake • Cylinder • Uncoated (Greenish color) • Coated w/Graphite (shiny black)
Ammunition • Powder (continued) • Powders burn at different rates • Gases and unburned grains are discharged upon firing • Grains can be found in clothing and skin
Ammunition Bullet • Originally lead spheres • Musket vs.. Rifle • Minnie ball (Capt.. Minnie, French Army) • Modern bullets • Lead • Metal-jacketed
Ammunition • Bullets • Various shapes • Round • Hollow point • Semi-wadcutter • Wadcutter
Bullet Comparison • Class characteristics • Number of lands and grooves • Diameter of lands and grooves • Width of lands and grooves • Depth of lands and grooves • Direction of rifling twist • Degree of twist
Bullet Comparison • Individual Characteristics • Imperfections on lands/grooves • Score the bullets • Jacketed bullets, more pronounced • Are peculiar to each firearm