Presentation on theme: "CRIMINAL INVESTIGATIONS AMMUNITION/ BALLISTICS. AMMUNITION Cartridge Structure –Cartridge Case –Primer –Head –Propellant –Bullet –Blanks- No Bullet."— Presentation transcript:
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
5.56 Centerfire vs. Rimfire
AMMUNITION Caliber Nomenclature –Rifled barrels Lands and grooves –Diameter of bore from land to land –Sometimes groove to groove diameter –Bullet diameter
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.
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.
Types of firearm weapons Non-rifled: only long Rifled: short and long
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. What happens?
Mechanism of injury: As the missile traverses the body it causes injury by: 1. Basic contact of bullet and its fragments (if present) with the tissue, so larger bullets create bigger damage at the same velocity. 2. Transferring some of its available kinetic energy to the tissue around it, so increasing velocity greatly increases damage. 3. 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.
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 its track severe disruption tissue pressure and more damage. So a 10mm wide bullet may cause a 15mm wide track of damage… SO…
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.
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.
Rifle bullet/pistol bullet
AMMUNITION Caliber Specification –U.S. System not consistent or accurate –.303 Savage =.308 bullet –.303 British =.312 bullet – 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: » »Some smokeless powder cartridges used this designation ».30-30
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 –All cases have stamps on bases –Imprinted for Identification Purposes Letters Numbers Symbols Trade names
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 Bullet Powder Weights –Grain = weight not granules –1 oz. = 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 (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
Ammo performance-Handguns CartridgeBullet gr.VelocityFt-lbs mm S&W ACP mag
Ammo performance-Rifles CartridgeBullet gr.VelocityFt-lbs x
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
Bullet Comparison Factors impacting Ind. Characteristics –Rusted barrel –Jacketed/unjacketed –Velocity/pressure –Bullets vary from lot to lot
Bullet Comparison Additional markings –Skid marks –Shaving Compositional Analysis –Fragments are recovered –SEM-EDX –Comparison between suspected guns bullets and recovered fragments
Bullet Comparison Base markings –Imprinted from propelled powder grains –Most evident in bullets w/lead base –Shorter barrel, deeper marks –Different forms produce different marks Spherical=circular pits Disk=circular imprints Black powder=peppered
Bullet Comparison Additional factors –Bullets fired in wrong caliber weapon –Decomposed bodies (Study after 66 days) Nylon clad-unaffected Aluminum-mildly affected Lead bullets, recovered from –Brain, chest cavity, abdomen-mild tarnish –Fat, muscle-severe oxidation-impaired match Copper alloy-severe degradation
Bullet Comparison Surface analysis of bullet –Non-organic material –Tissue analysis DNA typing
Cartridge Case Comparison Comparison MAY make ID possible –Type –Make –Model Test and evidence cartridges compared –Use same brand and lot Ammo consistency
Cartridge Case Comparison Markings=imprints or scratches –Magazine marks –Breech block marks –Firing pin marks –Size,shape, and location of; Extractor and ejector marks –Flute marks
Ballistics Ballistics=Study of motion of projectiles –Internal –External –Terminal Wound ballistics
Ballistics Forces –K.E.=1/2mv 2 –Velocity place larger role in force –Doubling mass, doubles force –Doubling velocity quadruples force –Energy transfer/loss
Ballistics Energy Loss/transfer –Amount of K.E. upon impact –Angle of yaw upon impact –Caliber, construction, shape –Density, strength, elasticity of tissue
Ballistics Movement through body –Crushes/shred tissue in path –Flinging, radially, surrounding tissue –Temp. cavity several times (12) size of bullet –Lasts 5-10 msec –Pulsates, contractions and collapse –+/- pressure sucks in bacteria/foreign materials
Temporary/Permanent Cavity –Max diameter of temp cavity is proportional to amount of kinetic energy lost –Occurs at maximum yaw or fragments –Yaw continues until Cg is forward or approx 180 degrees rotation –Size of cavity is determined by amount of K.E. lost by bullet –Size of cavity is determined to a degree by cross section of round
Ballistics Temporary/Permanent Cavity (cont.) –Compression, stretching, tearing of tissue –Handguns-Damage to area hit by bullet, very little collateral damage –Rifles-Radial damage to nerves, tissue, vessels, organs not struck by bullet –Damage related to density, elasticity and cohesiveness of tissue –Muscle vs. Liver vs. Lung
Energy loss along wound track –Not uniform –Changes and variations occur due to; Angle of yaw Change in density of tissue Change in structural dimension of bullet (mushrooms) –Fragmentation amplifies effect.223 marked yaw at 12cm Major frag/tissue disruption at 15-25cm
Critical velocity –At or above ft/sec (FMJ) –At or above ft/sec (expanding ammo) –Tissue damage more severe –Supersonic flow = strong shockwaves –Shockwaves travel through body –Damage is times larger –Due to higher amount of K.E. loss
Ballistics Critical amount of K.E. loss –Wounds are more severe –Exceeds elastic limits –Organ bursts –Projectile does not have to be near organ
Ballistics Critical amount of K.E. loss-Head –Special case –Cranial cavity is a closed, rigid structure –1% elasticity –No place for energy to disperse –Results in bursting injuries (high velocity)
Ballistics Temporary cavity size –10-12 times diameter of bullet –High K.E. loss times bullet Permanent Cavity size Handgun=smaller than round diameter High velocity=size of bullet Unless Elastic limit of tissue is reached=large irregular tearing wound track.
Case Study This case involved a barroom shooting. The incident went something like this:
Case Study Guy No.1- "Hey man, my quarters were up next!! I've got the next game on that pool table!!"
Case Study Guy No. 2- "Man youre crazy! I've had my quarters up there for over an hour!"
Case Study Guy No. 1- "Oh yeah? Well not only are my quarters up next but your breath stinks too!!!"
Case Study Guy No. 2- "You son-of-a- XXXXX!!!!! I'm gunna kill you!!!"
Case Study Me- "Now guys, calm down it's only a pool game; it's only a quarter."
Case Study Guy No.1 pulls out the Llama 45 auto below and points it at Guy No. 2.
Case Study In a drunken stupor he fires a single shot at Guy No. 2, missing him and hitting me right between the eye's with this 45 AUTO, 230 grain full-metal-jacketed bullet.
Case Study At the same time the pistol ejects the 45 AUTO cartridge case below into the corner pocket of the pool table.
Case Study Guy No. 1 and Guy No. 2 run out of the bar get in a car and go home. They tell mom they have been to the movies, hide the gun under their bunk bed and go to sleep.
Case Study Meanwhile back at the bar, a riot has ensued because the other guys with quarters on the table are really p off because the spent case has jammed the pool table. Order is finally restored when county police detectives clear the table.
Case Study My cold lifeless body is taken to the Medical Examiners Office for the 9 AM autopsy.
Case Study Guy's No. 1 and 2 are later roused from bed by Detectives and the pistol, it's magazine, and four 45 AUTO cartridges are recovered from under the bed.
Case Study The pistol, magazine, live ammunition, spent case, and bullet are later submitted to the lab for analysis.
Case Study Although my ex-coworker is all but overcome with grief, he manages to set aside his personal ties to the case and conducts the required analysis in a totally professional and unbiased fashion.
Case Study First course of business is to examine the pistol, which is found to be in perfect working condition. The pistol is test fired in the water tank and standards from the pistol are compared to the spent case from the pool table and bullet from my head.
Case Study The results of which are the match seen below.
Case Study Breech Marks: Standard from pistol (left) compared to the spent case from the bar (right).
Case Study Bullet land impression comparison: Standard (left) compared to "my" bullet (right).
Case Study By the way, Guy 1 "walks" when his brother testifies that I started the fight by stealing his brother's hot wings.
Case Study They really do have the best hot wings in town!!!
AMMUNITION Primers –Shapes Berdan –Anvil built in case Boxer –Anvil built in –Purpose –Fulminate of mercury Causes corrosion