Ballistics Flashcards
Define a round
A modern unit of ammunition
What are the components of a round?
Cartridge case, bullet, propellant, primer
What is the unit for measuring gunpowder and bullet mass?
the Grain
How many grains are in a pound of gunpowder?
7000
If 1kg = 2.2lb, how many grains are in 1kg of gunpowder?
15400 grains
Define caliber
The internal diameter of the firearm barrel, or the diameter of the projectile
What are examples of class characteristics?
- General firearm class
- General dimensions
- Make and model
- Shape of firing pin
What is proofing?
A process by which the unit is stressed around 30% beyond its normal operating pressures
What is the purpose of proofing?
To ensure the firearm can stand the rigors of normal use and is therefore safe for intended use
What is the general firing procedure?
- A live round is loaded through the breech into the chamber, which is then locked and closed
- When the trigger is pulled, a firing pin strikes the primer cup of the round, leading to ignition of the propellant
- Production of gas leads to increased pressure and at the optimum pressure, the bullet starts to accelerate down the barrel
- The firearm is then either manually or automatically cycled to remove the empty cartridge and insert another live round
What are the two main types of air weapons?
Spring and pre-charged pneumatic
What is rifling?
The formation of the spiral grooves that are formed in the barrel wall
Define lands
Raised section of barrel wall
Define landmarks
Sunken areas on the surface of a fired bullet
Define grooves
Sunken areas between lands in the barrel wall
Define groove marks
Raised areas on the surface of a fired bullet
Define twist direction
Rifling can be cut in either left or right hand configuration. If you look down the barrel, the rifling will be either clockwise or anticlockwise
Define twist rate
The number of revolutions per inch of the barrel length
Define described angle
Angle between the longitudinal bullet axis and inscribed rifling marks
Define broach cut
Uses a single point tool to cut one groove at a time, with each groove taking several cuts to reach the desired depth
Define electro-chemical etching
Uses an electrolyte, which is passed through grooves in a tool whilst in contact with the inside of the barrel to etch away the material and form grooves
What is chambering?
The length of the cartridge
What are the two possible outcomes if the wrong size round is used for a firearm?
- The round is too big for the chamber and either will not fit or will jam in battery after firing. This means the cartridge is stuck in the chamber
- The round is too small so will chamber but is loose in battery. The gun could explode as the cartridge will expand to fill the barrel, crack, and cause an explosion
Why are headstamps important?
Shows who made the ammunition. May reveal the caliber and manufacturers information
What does it mean if the firing pin mark is not central?
The weapon could have been altered or the incorrect ammunition was used
Why do self loading firearms not have protruding base rims?
To allow for stacking in a magazine
Why do single shot mechanisms have a protruding base rim?
To stop the cartridge falling through the cylinder of the revolver and cases are extracted via a central web, so need a rim
Define bullet
Any projectile below about 20mm in diameter that is fired from a barrelled weapon
Why do bullets have a lead and antimony alloy core?
The antimony reduces the malleability of the alloy and makes the lead core less easily deformed, it also increases the melting point
What is the purpose of jacketing?
To stop rifling drag in the barrel at higher velocities and to reduce acceleration deformation
What does unjacketed mean?
Lead alloy only, cheap, low muzzle velocity, low penetration, high impact deformation, prone to rifling smear at high muzzle velocities
What does semi-jacketed mean?
Includes a soft point, hollow point, and polymer tipped. Usually a bright brass jacket with a lead alloy core, less impact deformation than unjacketed, low penetration, high energy transfer
What does fully jacketed mean?
The entire bullet, except sometimes the base, has a bright brass jacket with a bonded or partitioned lead alloy core. Excellent penetration with low energy transfer, high stability, high energy retention, more expensive
What does IBIS stand for and what is it?
Integrated Ballistics Identification System
It is the automated firearms identification system
What is IBIS BRASSTRAX used for?
To create a 3D image of the cartridge case to look at the case, scratches, and firing pin marks
What does NABIS stand for and what is it?
National Ballistics Intelligence Service
It provides a confidential national IT system which identifies and tracks recovered ballistic items and records details of recovered items in sufficient detail
What is the path of the projectile dictated by?
Gravity, angle of launch, velocity, air density, temperature, humidity, projectile shape, drag coefficient, and projectile stability
When can we not use the ballistic equation?
When there is a height difference between the launch and impact sites
What is aerodynamic drag typically proportional to?
the square of the velocity
What properties contribute to drag?
The profile or shape of the projectile, the cross-sectional area of the projectile in the direction of travel, and air density
What is the centre of mass (CoM)?
the point where the bullet balances its weight. it is the only point of the bullet that follows the trajectory
What is the centre of pressure (CoP)?
the point where the aerodynamic forces act after adding all of them up
Why do bullets need gyroscopic stabalisation?
To overcome the want to tumble and keep the bullet pointed towards the impact point
What are the two important factors we must be aware of when it comes to the usefulness of wind tunnels?
- When air is being blown over an object at a specific velocity, aerodynamically, this is the same thing as the object moving through the air at that velocity
- We can use scaled up models of projectiles in the wind tunnel to measure the drag force and calculate the drag coefficients for that projectile’s design
Define sectional density (S)
the mass of the projectile divided by its maximum diameter squared
what does high sectional density mean for a bullet?
better impact effect
what is the ballistic coefficient?
a measure of the aerodynamic forces exerted on a particular bullet in flight
what is the unit of the ballistic coefficient?
kg.m^2
what is the spin rate (RPM)?
the rate of rotation of the bullet about its longitudinal axis after leaving the firearm’s barrel
what is aerodynamic lift?
where a ‘boundary layer effect’ occurs whenever air passes over a curved surface
what are the two types of wind deflection experienced by a projectile?
Aerodynamic and windage
what does aerodynamic wind deflection mean?
caused by wind flow over the projectile in flight, generating more lift on one side of the bullet due to spin induced pressure difference
what does windage wind deflection mean?
deflection caused by constant wind pressure during projectile flight
rifling-induced instabilities are caused by a low spin rate being experienced by the projectile. what are the three main causes? explain each
- low muzzle velocity - the bullet engages with the rifling but never reaches a spin rate that will ensure stability
- high muzzle velocity - the bullet velocity may be so high that the soft bullet skids over the rifling
- defective rifling - the bullet fails to engage with the worn or defective rifling, leading to low spin rate, aerodynamic imbalance, and potential tumbling
define yaw
refers to the lateral movement of the nose of the bullet away from the line of flight
define precession
refers to the rotation of the bullet around the centre of mass
define nutation
refers to small circular movement at the bullet tip due to the tip not being perfectly round
what are the main causes of yaw?
- a poorly cast bullet or bad loading, causing the bullet to be off centre in the cartridge case neck
- irregular rifling or non-optimal spin rate
Define reconstruction
The process of utilising information derived from physical evidence at the scene, analysis of physical evidence, and inferences drawn from such analyses to test various theories of the occurrence to prior events
Define re-enactment
A demonstration of a previously existing reconstruction based on conjecture rather than scientific principle
What are the four main possible outcomes when a bullet impacts a surface?
- The bullet remains intact and passes through, causing identifiable entry and exit holes (perforation)
- The bullet remains intact but does not pass through (penetration)
- The bullet does not remain intact and some, or all, of the fragments are either retained or pass through
- The bullet bounces off either intact or fragmented
What are some possible indicators for the use of a firearm?
- Bullets, cartridges, or fragments
- GSR deposits
- Wipe ring around hole
- Size and shape of the hole
- Evidence of high energy penetration and damage highly local to the hole
What are the results of metal being shot at?
- Usually leave a near margin on the entry side of the hole
- Exit side will look like a truncated funnel
- May be a wipe ring on the inside of the funnel
- Length and width of the funnel depends upon caliber and projectile velocity, physical characteristics of the metal, and bullet construction
- Will just be a dent if the metal plate is thick
- Paint or other surface coatings may be disrupted
What are the results of wood or frangible material being shot at?
- Tend to present a neat hole on the entry side
- Likely to be cratering or splintering on the exit side with widely distributed debris
- Low velocity, large caliber will cause significant splintering in the exit side
- Soft wood splinters harder than hard wood
- May be a wipe ring towards the entry side
What are the results of glass being shot at?
- Can figure out order of bullet impacts as radiating cracks will not propagate across an existing fault
- High velocity bullets tend to leave small, neat holes with little fracturing
What are the results of fabric being shot at?
- GSR will be present if it is relatively close-range shot
- For synthetic fabrics, microscopic examination at the edge of the hole will show evidence of individual fibres melting resulting from the frictional heating caused by the bullet’s transit
- For natural fabrics, microscopic examination will reveal fibres with shredded and frayed ended around the hole
What is some evidence from a firearm user?
- Flash burns on user and target, including GSR on skin or target
- Burns to fabrics and flammable surfaces
- Imprints and impressions
- Hearing damage
What is a slide bite?
Where the recoiling slide on SLP cuts the web between the thumb and index finger on the hand holding the weapon. This is from holding the firearm too high on the pistol grip
What is a hammer bite?
SLPs with an external hammer can pinch or abrade the web between the thumb and fingers. A mark may be present that can be matched specifically to the hammer
What are recoil marks?
Marks made from recoil when weapon is not held correctly
What is a scope bite?
Where the ‘eye relief’ leaves a characteristic crescent-shaped contusion on the forehead or nose of the shooter
What are the information/evidence types to help with placing the shooter in the scene?
- Eyewitness accounts
- Bullet trajectories and velocities
- Gunshot residue
- Cartridge ejection patterns
Define ricochet
The change in angle and/or direction of a projectile resulting from substrate contact
What are the two main forms we come across of GSR?
- Particulate - for which we collect it with aluminium stubs with a sticky carbon coating
- Precipitate - for which we would swab with distilled water and/or ethanol and then extract the particles with fine filters
What is tattooing?
When GSR leaves permanent tissue markings
Cartridge ejection patterns from a firearm are dependent on many factors. What are these?
- Weapon design
- Weapon condition
- Ammunition type
- Position weapon is held when fired
- Movement of weapon during firing
- Type of terrain where shooting occurred
- Presence of obstacles at scene
What are the difference in entry and exit sites of a wound?
Entry site - bullet wipe, abrasion rings, comparatively small bullet hole, inwards bevelling of skull
Exit site - potentially larger bullet hole, outwards bevelling of hole, material is projected outwards, may not be directly opposite from the entry wound
What did the 1903 Pistols Act outline?
- It was the first legislation to try and restrict the sale and ownership of firearms
- It defined a pistol as a firearm whose barrel did not exceed 9”
- The act made it illegal to sell or rent a pistol to anyone unless they could produce a current gun license or game license
- Rather ineffective as anyone could go to the Post Office and purchase a license
What did the 1920 Firearms Act outline?
- The Act required anyone planning to purchase or own a firearm or ammunition to obtain a firearm certificate first
- Certificated lasted for three years and specified the weapon and maximum amount of ammunition the holder could acquire
- Local Police Chief Constables decided who could hold a certificate
- Applicants were required to demonstrate they had good reason to own a certificate
- Initially the act ignored smooth bore weapons
What did the 1937 Firearms Act outline?
Amended and updated some of the provisions of the 1920 Act. The main updates included:
- Raising the minimum age for buying a firearm to 17
- Brought shotguns and other smooth bore weapons with barrels of less than 20” into the legislation
- Produced the requirement for gun dealers to be licensed
- Chief Constables could add conditions to firearm certificates
- Self-defence was no longer appropriate grounds for owning a firearm
- Banned the private ownership of fully automatic weapons
What did the 1968 Firearms Act (Current Legislation) outline?
This unified and rationalised all existing firearms legislation in a post WW2 context. It created three main firearm classification groups:
Section 1 - firearms
Section 2 - shotguns
Section 3 - prohibited weapons
What are the good reasons for possessing a weapon or ammunition?
- Member of a gun club
- Sporting pursuits
- Land management
- Professional/work requirements
How should firearms be stored?
In a secure gun cabinet with ammunition stored in a separate locked area
What is the consequence of jail time in owning a firearm?
3+ years - permanently prohibits
3 months to 3 years - five-year ban
What are the four definitions of a firearm?
- A letal barrelled weapon –> a barrelled weapon from which a shot, bullet, or other missile, with kinetic energy of more than one joule at the muzzle of the weapon, can be discharged
- A prohibited weapon
- A relevant component part in relation to a lethal barrelled weapon or prohibited weapon
- An accessory to a lethal barrelled weapon or prohibited weapon where the accessory is designed or adapted to diminish the noise or flash caused by firing the weapon
What is ammunition ‘defined’ as?
Ammunition for any firearm and includes grenades, bombs, and other like missiles whether capable of use with a firearm or not and also includes prohibited ammunition. This does not include ingredients and components of ammunition
Under Section 1, it is an offence for a person…
- To have in his possession, or to purchase or acquire, a firearm to which this section applies without holding a firearm certificate in force at the time, or otherwise than as authorised by such a certificate
- To have in his possession, or to purchase or acquire, any ammunition to which this section applies without holding a firearm certificate in force at the time, or otherwise than authorised by such a certificate, or quantities in excess to those so authorised
What firearms does Section 1 not include?
- A shotgun within the meaning of this Act
- An air weapon and which is not a type declared by rules made by the Secretary of State under Section 53 of this Act to be dangerous
Section 1 applies to any non-prohibited ammunition for a firearm, except…
- Cartridges containing five or more shot, none of which exceeds 0.36 inches in diameter
- Ammunition for an air gun, air rifle, or air pistol (unclassified)
- Blank cartridges not more than one inch in diameter measured immediately in front of the rim or cannelure of the base of the cartridge (unclassified)
What type of firearm does Section 1 mainly cover?
Bold-action rifles but also any other single shot mechanisms
What other firearms does Section 1 also include?
- 0.22” caliber rim-fire rifles, where semi-automatic and pump action mechanisms are permitted with no magazine limit
- Smooth bore revolver guns chambered for 9mm rim-fire or is designed to be muzzle loaded
What are the measurements for Section 1 firearms?
- Barrel is longer than 30cm
- Overall length of the firearm is longer than 60cm
What does Section 2 refer to?
Shotguns
A shotgun within section 2 of the act is a smooth-bore gun which…?
- Has a barrel not less than 24 inches in length and does not have any barrel with a bore exceeding 2 inches in diameter
- Either has no magazine or has a non-detachable magazine incapable of holding more than two cartridges
- Is not a revolver gun
What does Section 5 cover?
Prohibited weapons
What are some examples of prohibited weapons covered in Section 5?
- Military and Police hardware
- Any firearm disguised to look like another object
- Automatic weapons
- Handguns
- Anti-tank rockets, grenade launchers, missiles
- Semi-automatic weapons
- Prohibited ammunition
What are the 5 special exemptions from Sections 1-5?
- Police permit to use firearms issued by chief police officer for the area
- Carriers, auctioneers, etc
- Authorised dealing with firearms
- Slaughter of animals
- Sports, athletics, and other approved activities
What is the law for the use of air weapons? state ages
- Anyone over the age of 18 can purchase an air weapon that is not ‘specially dangerous’ and use it on private property
- 14-17 year olds cannot buy or own air weapons but can use them on private land without supervision
- Under 14 year olds cannot buy or own air weapons but can use them on private property with supervision
What is no certificate required for?
- Air and gas operated rifles with less than 12 ft-lb in muzzle energy
- Deactivated firearms
- Shotgun cartridges containing 5 or more shot, none of which exceed 0.36 inches in diameter
- Display boards and decorative items
What is does Section 8 of the 1998 Firearms Amendment Act define a deactivated firearm as?
- It is incapable of discharging any shot, bullet, or missile
- It bears a mark and is certified in writing by a person approved by the Secretary of State
What are the three stages of the internal firing process?
Lock time, ignition time, and barrel time
Define lock time
Time between the activation of the firing mechanism and ignition of the primer charge
What is the trigger mechanism?
Usually a wholly mechanical system which links the trigger to the firing pin assembly
How does the trigger mechanism work?
Consists of a system of levers, known as sears, which hold the firing pin or hammer under spring pressure until the trigger is operated
What happens to the firing pin spring when the firearm is ‘cocked’?
The spring is compressed and then mechanically held by a sear. The energy stored within the spring is then released when the trigger is puled and is used to activate the primer
How does the trigger safety mechanism?
Physically blocks the external trigger action
What is the problem with the trigger safety mechanism?
The rest of the firing mechanism is free to operated and so if dropped, the sears can move and the firearm can be shot
What is the sear safety mechanism?
Blocks the action of one or more of the trigger sears
What is a problem with the sear safety mechanism?
Failure will allow the firing pin to move independently
Define a sear
Any mechanical part of a trigger mechanism that has a sliding contact surface
How do grip safety mechanisms work?
They must be compressed before the weapon will fire. By their nature, they are always sear engagement mechanisms
What is a magazine interlock?
An internal mechanism that engages a mechanical safety when the firearm’s magazine is removed
What is the purpose of the magazine interlock?
It is designed to prevent accidental discharge where the magazine has been removed but a round is still chambered
What is the firing pin safety?
A mechanical system that blocks the action of the firing pin
Why is the firing pin safety the most reliable and effective form of safety catch?
It is unaffected by operation of the trigger and trigger sears
What is the test method for safety failure?
- Ensure the unit is loaded
- Cock the action and dry fire it repeatedly
- Then re-cock the action and subject the unit as a while to low velocity impacts in all three planes
- Operate the trigger with the safety engaged
- Operate the firearm in the same way as when the incident occurred
- Repeat the process 10 times
Define ignition time
The time from activation of the primer charge to initial movement of the projectile
What are the four factors which influence ignition time?
- Primer type
- Propellant design
- Chamber dimensions
- The ‘tightness’ of the bullet in the cartridge neck
How does primer type effect ignition time?
The time this process takes depends on how sensitive the primer is and how quickly it detonates
How does propellant design effect ignition time?
Rate of reaction and burning of the propellant, generation of pressure as propellant burns
How does the ‘tightness’ of the bullet in the cartridge neck effect ignition time?
We want pressure to be able to build
What is barrel time?
The time from first movement of the projectile to when the projectile exits the muzzle
What is barrel time dependent on?
- Projectile shape, size, and mass
- Internal barrel function
- Rifling type and rate of twist
- Chamber pressure and propellant burn rate
