Firearms and Toolmarks Test # 2
Rim fire only survives as _______ caliber
.22
When were Berdan and Boxer primers invented?
1860's
Cartridge nomenclature
2.2.6
Pointed Bullet
A bullet with a long point that will hold its velocity and energy over a great distance
Rim fire
A flange-headed cartridge with the priming composition in the hollow rim
Boat Tail bullet base
A tapered rear end of the bullet, designed to decrease drag for long distance accuracy, usually greater than 200 yds
Why is black powder hard to use?
Absorbs atmospheric water, ignites easily by static electricity, and low impact ignition tolerances
------------- ----------- acts as a fuel to prolong burning time
Antimony Sulphide
Boxer Primer
Anvil is a small bent disc of steel INSIDE the cup making the primer completely self contained; centrally located flash hole
Flat Base
Base perpendicular to the sides of the bullet
Flat Bullet Base
Base perpendicular to the sides of the bullet
Tear Gas Cartridges
Blank ammunition containing lachrymatory/sternutatory substance either CN or CS gas
Obturation
Block up of the chamber; expanding and sealing of chamber during firing
Belted Cartridge Case
Cartridge case designed to provide positive headspacing and allow magazine feeding
Straight cased cartridges
Case diameter is approx the same along its length
Concave Bullet Base
Central Indentation
Concave Base
Central indentation
Early Black Powder contained _________.
Charcoal, sulfur and potassium nitrate
Berdan Primer designed by __________ _________ of the US Army Ordnance Department
Col Berdan
Boxer Primer developed by ____ ______ of the Laboratory at the Royal Woolwich Arsenal, England
Col Boxer
Compound Base
Combination of boat tail & recessed
Semi-rimmed Cartridge Case
Combination of rimmed and rimless design
Rebated Cartridge Case
Designed to allow a larger diameter case while using a smaller bolt face; e.g. .284 Winchester
What can you do to analyze a bullet with no lands and grooves?
Elemental analysis; can be matched to the ammunition in the possession of a suspect
Rimmed Cartridge Case
Flange larger than the diameter of the body of the cartridge case, holds the cartridge in place and stops the travel of the case into the chamber. Provides for easy extraction. Used mostly with revolvers.
Rimless Cartridge Case
Flange same size as diameter of the cartridge. Allows for smooth feeding from magazines
Internal Firing Pin Safety
Found in many semi-automatic pistols. When the trigger is forward a small internal plunger is blocking the pistol's firing pin. Pulling the trigger pushes the plunger up to unlock the firing pin
Where do you mark the weapon?
Frame, barrel, cylinder
________________ bullets are widely used to reduce target damage and prevent ricochet
Frangible
Spitzer
German term applied to an elongated pointed arch bullet with sharp point
Locked Breech Safety
Guns designed to fire from a closed and locked breech have block or interrupt safety
Boxer Centerfire
Has a single internal anvil, with one flash-hole. This allows convenient reload ability since the primer is easily punched out through the flash hole
Thermodynamic Energy
Heat is produced, for rapid burning and expanding gas
Ball Burnishing
High Quality Rifles; repeatedly pushing steel ball bearing of same size as the barrel lands through the bore
Expanding Nose Bullet Types
Hollow point; jacket cuts; thinning jacket near nose; using a double jacket; notching around jacket in a ring; hard metal wedge; slitting the jacket longitudinally; covering nose with aluminum
Interial (Floating) Firing Pin
Incorporates firing pin whose length is too short to span the distance between the forward most position of the hammer and the primer of a chambered cartridge and which is usually restrained in the rearmost position
-------- ------- is the sensitive explosive ingredient in primer
Lead Styphnate
Lead Fouling
Lead comes off the bullet in the barrel and may get blown out of the barrel
Twist Pitch
Number of inches of barrel for a complete turn of the bullet
____________ ammunition prevents lead fouling, reduces lead contamination, and reduce friction with the bore to enhance velocity.
Nyclad
Out of Favor Priming cartridges
Pinfire, lip fire, cup fire, teat fire
Berdan Primer
Primer cup contains only the priming mixture and the anvil is part of the cartridge case
Modern Smokeless Powder
Produces higher velocities, and produces less fouling of the barrel, with less smoke than Black Powder.
Heeled bullet base
Rear of the bullet is reduced so that the case diameter is the same as the driving surface; .22 caliber
How does hollow point bullets improve stability?
Removing material close to the axis shifts some of the mass out from the axis, increasing gyration
___________ cartridge case design depends on accurate case length
Rimless
____________ cartridge case designs are not well suited for use in box magazines
Rimmed
What are the three types of crimps?
Roll, Taper, Stabbed
Secondary Automatic Safety
Safety feature which requires no action on the part of the shooter to engage the disabling feature
What is the purpose of a crimp?
Securely and uniformly hold the bullet in the cartridge case
Recessed Base
Shallow, flat bottomed central indentation
Recessed Bullet Base
Shallow, flat-bottomed central indentation
What is the difference between "Boxer" and "Berdan" primers?
Size; internal construction; American vs European
Meplat
Small flat area on a pointed bullet to make it easier to handle and protect than a sharp point
Boat Tail Bullet Base
Tapered rear end of the bullet, designed to decrease drag for long distance accuracy, greater than 200 yds
______________ is a highly sensitive explosive chemical used in modern priming compounds
Tetrazine
Berdan Centerfire
The central anvil is part of the cartridge case. Usually two small flash holes on either side of the anvil. Not intended to be reloaded.
Foster Slugs
The defining characteristic of ____________ ______________ is the deep impression in the base; drag tends to push back into straight flight
Headspacing
The physical distance between the breach of the weapon and the design feature keeping the casing from going through the barrel
Burning Rate
The smaller the grain, the faster the burn; handguns require faster burning powder
How does hollow point bullet reduce stability?
Transfers the center of gravity further to the rear
Battery Cup
Used in the shotgun ammunition
Full Metal Jacket Bullet
Usually copper nickel alloy
Exposed Core Base
Visible lead core, surrounded by bullet jacket
Exposed Core base
Visible lead core, surrounded by bullet jacket
What is corning gunpowder?
Wetting it, compressing it, drying it, and grinding it again for more efficient powder
Rebounding Hammer
When the trigger is released after firing, the hammer moves slightly rearward from the fully-forward (fired) position, AUTOMATICALLY introducing a gap between the firing pin and the primer at which point it is blocked from further forward movement without further manipulation of the trigger
Why should you not use a flat bullet for distance shooting?
Wind resistance will cause it to have a tendency deflect off course
Geco
Zinc and titanium based primer (1980's)
Remington Accelerator Cartridge
a cartridge that utilizes a smaller bore diameter projectile held in a bore diameter sleeve
Saboted Bullet
a sub-caliber bullet surrounded by plastic, which is discarded as soon as the projectile leaves the barrel
Neutral Burning Powders
allows burning from inside and outside; burning stays more constant
Higher velocity ammunition contains ___________ to harden the lead
antimony
Physical energy
as hot gases push the projectile, it reacts to the friction and causes torque, recoil, and barrel whip
Chemical Energy
as the propellant converts or decomposes almost completely into a gas.
Hatton rounds are made for ___________
breaching of doorways
Roll Crimp
case neck rolled either into the bullet material or a groove in the bullet to secure it
Remington accelerator cartridges prevent the bullet from touching rifling; what does this do?
causes cartridge to be covered by L&G marks
Where do you mark revolvers?
chamber under the hammer, note where cartridge positioned in the cylinder, note whether the cylinder rotates to the left or right
hammer block safety
common to revolvers with hammer-mounted firing pins from moving through the frame; requires trigger pressure to stay down
Cordite
contains 37% nitrocellulose, 58% nitroglycerine and 5% vaseline
Brenneke slugs
deform less and provide deeper penetration than foster slugs; short range
Transfer Bar
design feature intended to automatically prevent the hammer from contacting the firing pin by introducing a "bar" between them which when impacted by the hammer "transfers" the energy to the firing pin
Hammer Block
differs from the transfer bar in that the falling hammer will impact and come to rest short of the firing position on an otherwise non-functional feature of the assembly unless that feature's blocking action has been removed through the sustained rearward pull of the trigger
Frangible
disintegrate at impact; powdered metal (iron) shaped like the nose
Half Cock
ensures the hammer cannot come in contact with the firing pin
The smaller the grain the _____________ powder burns.
faster
Skid marks
fired from a revolver; short length of rifling on the bullet appearing to be parallel with axis
Wadcutters
flat nosed bullet with a sharp shoulder, to punch out holes in target paper
Hollow Point
generally semi-jacketed; designed to expand on impact with soft targets thus increasing the wounding effect
Degressive Powders
give peak pressures when the bullet is close to the breech and low muzzle pressure; holes
Hook Cutter Rifling
hardened steel cutter is set into a recess in a steel rod of slightly smaller diameter of barrel; as dragged through bore, barrel is rotated; each pass cuts one groove and must be rotated
Flakes (powder)
have a large surface area to burn; preferable for short-barreled, small caliber weapons
Magazine safety
intentional disabling of gun left unattended
Semi-jacketed Bullet
jacket on the side where it comes in contact with the barrel, for high velocity, but still lead at the tip
Stab (ring) crimping
jacketed ammunition; consists of several impressed dimples or a groove pressed into the case mouth by a collet
What does FAAS detect that NAA methods do not?
lead
Lead Lapping
lead plug the same diameter as the bore is repeatedly pulled through rifling whilst being washed with fine abrasive
Identify Hook Cutter Rifling due to?
longitudinal striations in the cut grooves and similarity of micro stria in each of the grooves since same tool is used
Pure Lead bullet noses are only used in ______ _____________ ammunition.
low velocity
Progressive Burning Powders
multi-perforated particles; peak pressure at a point in bullet travel further along muzzle
Transfer bar safety
must be in the up position for energy to be transferred from the hammer to the frame mounted firing pin
More reliable methods for gunshot residue detection include __________________ (NAA), ________________ (FAAS), X ray fluorescence, and photo luminescence techniques.
neutron activation analysis, flameless atomic absorption spectroscopy
Gunshot residue detection methods such as color test for __________ and color tests for _________, ___________, and ___________ have been replaced in recent years.
nitrates; antimony; barium; lead
Sliding Button Safety
operated by a sliding motion ans is typically located on the left side of the firearms frame; when engaged, this safety can block the trigger and can disengage or block the internal gear
Cross Bolt Safety
operated by lateral force on a button, usually located on the trigger guard, prevents the trigger from being pulled
Barium Nitrate primers provides ____________ to increase the temperature of the flame.
oxygen
Wadding
plastic, paper, or fiber material designed to separate the shot from the gunpowder; protect the shot as it is pushed down the barrel
Firing Pin Block
positive blocking of the firing pin preventing its forward movement and which is only removed by sustained trigger pull
Taper Crimp
primarily with cartridge that headspace on the case mouth with lead bullets
Barium, antimony and lead are commonly found in __________ residues.
primer
Pyrodex
propellant introduced in 1970s with similar burning characteristics to black powder but less of the downfalls
Heeled Bullet base
rear of the cartridge case is reduced so that case diameter is the same as the driving surface, usually .22 caliber
Foster slugs may also contain ____________ to allow slug to be swaged down when fired through a choked shotgun barrel
rifling
Grip Safety
secondary safety feature where gun is firmly grasped
Scanning electron microscopy (SEM) makes it possible to establish the __________ and _____________ of the individual gunshot residue particle.
shape; appearance
Foster Slug
short round nosed bullet with a deep cup in the base
Handgun require faster burning powder because of their _____________ ______________.
shorter barrels
The __________ of the case stops travel of the cartridge into the chamber
shoulder
Shotgun slug
single projectile primarily designed to be fired from a smooth-bored shotgun
Trigger safety
small extension on the forward edge of the trigger which must be depressed before the trigger can be pulled
Single-based powder
smokeless propellant by dissolving nitrocellulose with ether and alcohol
For tape collection of gun shot residue SEM tests, important that tape is sticky and ________.
smooth (ensures small particles can easily be observed)
Brenneke Slug
solid lead, pre-rifled projectile with an attached plastic, felt or cellulose fiber wad; provides drag stabilization by moving the centre mass forwards
Buckshot is poor at penetration due to the ____________ __________
spherical shape
A hollow base to a bullet moves center of gravity ___________ the nose, _________________ stability.
towards, increasing
Thumb Safety
usually located on the side of a pistol, it can block the hammer from striking the firing pin, will sometimes de-cock the pistol's hammer, and can disengage the trigger mechanism
Bottle-necked
wide bodied case is reduced in diameter to that of the bullet permitting a larger volume propellant to be used
Tapered case cartridge
wide-based cartridge case is gradually reduced in diameter along its length