Fouling: Soot, residue of completely burned powder, dust-like, wipes off
Stippling (tattooing): Unburned powder and debris, causing punctate abrasions on target. Larger and heavier so travels farther. Does not wipe off.
Margin of abrasion: Characteristic of enterance wound but can be seen in shored exit.
|Range of Fire:
Contact: muzzle of gun touches target
– Tight: fouling in tissue, muzzle stamp
– Loose: fouling on skin and in tissue, searing
Close: <6″ Stippling & Fouling
Intermediate: 6-30″ Stippling
Distant: >30″ Neither
(Distances approximate and depend on many variables. For accurate assessment need to test fire weapon with ammunition used.)
|Enterance: margin of abrasion, round or oval defect, size usu smaller than bullet (elasticity of skin), +/- fouling/stippling
Fouling/Stippling may be absent: clothes, hair, blood washes away soot, handling, efficient ammunition, type of powder.
Longer the barrel, further soot will travel; fouling with handgun seen with naked eye if fired up to distance of 2x barrel length
False Stippling: Suture removal, broken glass, insects, shotgun packing
Keyhole skull wound: shallow angle shot where bullet splits into 2 fragments
Graze: skin tags point to gun
Extent of injury depends on energy lost in the body
KE = 1/2mv^2
Kinetic Energy Lost depends on: amount of KE before impact, angle of yaw (means the bullet destabilizing along central trajectory axis, as opposed to wobble, which is end-over-end tumbling; wobble usually occurs only after impact with intermediary target), bullet & density of tissue
Hollow Point: tend to stay in body or break up if they hit a hard surface; no visible difference in wounding (most KE from velocity, not mass).
If jacket separates, seldom leaves body. Aluminum jackets can’t be seen on X-ray.
Jackets carry rifling marks.
Cartridge cases: id type, make & model of weapon (class characteristics); other markings include magazine markings, breech-block mark, ejector and extractor marks, firing pin mark.
Revolver: cocking hammer revolves cylinder. Colt rotates clockwise; Smith & Wesson, counter-clockwise
– Gap between cylinder and barrel may see “cylinder gap” fouling or stippling on an object adjacent to gap when gun fired.
– Uses lead bullets: round, semi-wadcutter, hollow point, wadcutter
Semiautomatic: holds a cartridge in the chamber and rest in a clip; forces generated by fired round operate the mechanism that loads next round.
– Uses jacketed bullets to prevent jams from lead particles.
– Trigger pull is force (usu 12-15 lb) needed to fire the weapon; a “hair trigger” needs less.
Rifled long gun that is fired from the shoulder
Barrel is rifled with lands and grooves (like a handgun).
Typical rifle 30″ barrel; Carbine = shirt rifle 18-24″ barrel; legal minimum 16″ barrel.
High velocity > 2000 ft/sec
Lead snow storm on X ray = high powered rifle with semijacketed bullet, typically a hunting rifle
Submachine gun/pistol: fully automatic weapon that fires pistol ammunition.
Machine gun: fully automatic weapon that fires rifle ammunition.
Caliber: diameter of bullet or bore measured from land to land (to convert mm to inches, multiply by 4 e.g. 9 mm = 36 caliber)
Jackets: copper/zinc; copper/nickel or aluminum
There is a copper wash, “gliding” on some .22’s
Rifle: full metal jackets (military) or hollow or soft point partial jacket (hunting)
Frangible: .22 caliber bonded iron or lead; used on cattle and on firing range. Breaks up on impact and cannt discern rifling Penetrates skull up to 36″. No ricochet.
Glazer: (“Short Stop”): bullet with shot that opens on impact. Little injury > 25′. Copper cup filled with lead shot and capped with Teflon or nylon. Penetrates body 6-8″. In body find metal fragments with teflon cap and copper casing.
Sabot/Accelerator: Sabot is the sleeve that converts a bullet core to the same size as the gun. Armor piercing tungsten carbide core sits in plastic Sabot (has slits and petals 5-6 and falls off bullet after exits muzzle (approx 14″, but can travel 50′). Rifling is on Sabot. Accelerator round is a subcaliber bullet fitted into a larger caliber cartridge with sabot.
Nyclad: Nylon coated lead bullet. Must recover nylon for bullet comparison. No rifling on lead, only on nylon.
KTW: “Cop Killer” Teflon coated tungsten or steel with copper jacket base (jacket has rifling).
Super Vel: Favored by police. Increased damage. .38 partial jacket, high velocity. Flat or hollow point. 1370 ft/sec.
Tandem Bullets “Piggy Back”: Examine bullets
Golden Sabre, Starfire, Black Talon: Petals open like claws
Plastic: Can pierce skin from contact to 20′ creating a superficial circular laceration
Nitrocellulose (smokeless), various shapes (ball, flake, cylindrical)
Primer: LAB: Lead (Pb), Antimony (Sb), Barium (Ba)
Primer detection tests:
– Walker test: nitrates in clothing by blotting on photographic paper
– Paraffin/Dermal Nitrate Test: Gonzalez 1933 (diphenylamine -> blue)
– Harrison-Gilroy: triphenylmethylarsonium iodide (Sb) + Na-rhodizonate (Pb and Ba)
– Neutron activation (detects Sb & Ba; misses lead, need FAAS)
– FAAS (Flame Atomic Absorption Spectroscopy): to be + need all three with values of Pb >800 ng, Ba 150 ng, Sb > 35 ng.
– SEM-EDX: Scanning Electron Microscope with Energy Dispersion X-ray Analysis: shows shape and elemental analysis (90% of handgun fireings)
|SHOTGUNS: Smooth bore long gun that fires multiple balls encased in a plastic tube with wad (plastic or cardboard) separating shot from gunpowder. May also fire a single projectile called shotgun slug.|
|Guage: barrel caliber. # lead balls of a certain dameter that weigh 1 pound. Has nothing to do with size of shot in the cartridge.
Wad: On Xray faint circle (due to thin coat of lead); enters body at 8 -10 feet and can travel up to 50′
Choke: degree of narrowing of barrel to control spread of shot. For first 10 feet there is no choke effect. 12, 16 and 20 full choke all have the same pattern at the same distance.
|Shot: Two categories of size, Bird and Buck; smaller # = larger diameter
Guage has nothing to do with pattern size (increased guage only increases density).
Remington – plastic cup, 4 petals (need 1 foot distance to open), petal mars at 1-3 feet
Winchester – cup wad, 2 cushions (cardboard wad can hit body from as far as 15 feet)
Federal – plastic cup [.410 all have 3 petals].
Magnum: contains more shot and more powder, but same velocity
Rifles (4 or 6 lands and grooves)
Smith & Wesson handguns (5 lands and 5 grooves)
rimfire: firing pin impression is very important.
|Guns that do not produce or do not have reproducible rifling:
– Revolver without barrel (get bullet with flared base)
– Smooth bore rifle and pistols
– Zip guns (car antenna)
– Sympathetic discharge (cheap rim fire guns set off adjacent chambered bullet)
– Gun with bullet of smaller caliber (skid marks)
– Heckler and Koch: polygonal boring makes it difficult to compare bullets
– Rusted barrels will have rifling but subsequent firings may have different markings.
|Pink color of muscle around enterance wound: CO in gunsmoke makes carboxyHb; perf of lung w/oxygenated blood may also do this (oxyHb).|
shotgun wound with scalloping and 2 -3 separate pellets (range)
enterance vs. shored exit
Shotgun 10 -20 ft range
X-ray of air pellet
pseudostippling from a suture
stippling: flake vs. ball powder
0.410 shotgun: 3 petals on skin
Bullet: 0.25 vs. KTW vs. Glazer (metal fragments with Teflon cap and copper casing in body).
Black talon – hollow point
Kinetic energy of various velocity and grain bullets
Velocity of a .38 needed to penetrate skin