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.
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. = 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
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 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
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 2625-2953 ft/sec (FMJ) –At or above 1500-2000 ft/sec (expanding ammo) –Tissue damage more severe –Supersonic flow = strong shockwaves –Shockwaves travel through body –Damage is 20-30 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-20-30 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 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.