FS 8 - Firearms

What are factors that go into firearm accuracy?

- Accuracy of a firearm can be improved greatly by lengthening its barrel - Rifling within the bore of the firearm imparts spin upon the projectile, resulting in improved accuracy - Lands (the area between the grooves) and grooves in the rifling imprints different scratch patterns on the bullet, which can be used to identify the weapon's manufacturer

What are the different types of ammunition?

- Bullets have a parabolic front and a wind-splitting shape - Cartridges (rifles and handguns) - primer, gunpowder (smokeless powder), bullet Shotgun shells - Bore-size projectile (slug), pellets of large shot, or many tiny pellets (BBs)

What are handguns?

- Compact weapon that can be fired by using one hand - Delivers multiple shots before it needs to be reloaded. - Have shorter barrels and can be more easily concealed. - Controlled by authorities in most states. - Most commonly encountered types of handguns are revolvers and semiautomatic pistols.

What are shotguns used for?

- Designed to shoot a large number of small pellets that disperse into a circular pattern - May disperse over a 20-yard-wide area - Consist of a long barrel and a butt stock - Barrel does not contain rifling, so projectiles are not marked with rifling characteristics - Diameter of barrel is expressed in gauge - Criminals may modify by cutting down the barrel and the stock, making it easier to conceal

What are silencers?

- Device attached to a handgun to reduce the amount of noise generated by firing - Fitted into the barrel with internal baffles - Criminals may also shoot thorough pillows and empty plastic soda bottles to reduce noise

How is ammunition preserved and collected?

- Each fired bullet or cartridge case found at a crime scene should be packaged separately in a paper envelope - Use only rubber or plastic coated objects to remove bullets from building materials

What do investigators do to take records of guns? What are the two most common methods for restoring serial numbers?

- Every gun manufactured has a serial number stamped into the metal of the gun's frame, others in a number of locations - Licensed gun dealers must maintain records. - 15% of all recovered firearms every year have had their serial numbers removed, or partially removed because criminals often try to destroy them to prevent the police from tracing the weapon. The most common are the magna flux method and acid etching method

How is firearm evidence collected and preserved?

- Examine, unload, and clear for removal. - If the firearm was loaded, the number and type of rounds should be noted. - If its a revolver, a diagram should be made with each chamber being designated with a number, its position should be marked on the diagram and the position of spent and unfired cartridges noted.

What are submachine guns?

- Guns that can fire automatically like a machine gun but use pistol ammunition - Small and lightweight - Issued to special forces of the military, government official guards, and police units - Not very accurate at moderate distances, but very effective in close-quarter combat

What are rifles?

- Guns with long barrels and a butt stock - Difficult to conceal, and greater effort required to carry them - Much more accurate than handguns - Come in single-shot and multiple-shot models.

What are two types of automated ballistic comparisons?

- Integrated ballistics identification system - National integrated ballistic information network

What are semiautomatic pistols?

- Make use of the recoil generated by the fired cartridge to operate, which ejects the empty cartridge case, loads the next cartridge, and cocks the hammer. - Reduced the time needed to fire multiple shots - Carry 15 to 19 rounds - More prone to jam, and requires more practice

What increases the force of the bullet?

- The force delivered by a bullet is proportional to the kinetic energy imparted to it. - As the caliber (internal diameter of the barrel) of the weapon increases, so does the kinetic energy of the bullet fired from the gun. - The larger the caliber, the wider the bore of the barrel, and the larger the bullet needed to fill the bore. - The greater the caliber, the greater the mass of the projectile.

How is firearm determined?

- The number of lands and grooves, the caliber, the direction of the twist, and the width of the lands and grooves - Caliber can be determined by measuring the bullet's diameter or weighing it - Known bullet and suspect bullets are placed under a comparison microscope where the examiner rotates items in an attempt to find matching striations or determine that no such match exists

What are the four categories of firearms? What are the four problems firearm technology focuses on?

- handguns - shotguns - rifles - submachine guns - delivering the projectile accurately - increasing the force delivered by the projectile - increasing the rate of firing - improving the reliability of the firing mechanism

What are the advantages and disadvantages of revolvers?

Advantages: - less expensive, simpler, more reliable, easier to use, more accurate. Disadvantages: - typically limited to six-shots, take more time to reload, and require a more forceful trigger pull

What parts of cartridges are examined?

Caliber, location of the weapon's firing pin and its size and shape, and the sizes of extractors and ejectors - The individualisation of cartridges is possible because the cartridge case is imprinted when the gun is fired

What is a flintlock rifle? What are its disadvantages? How were these disadvantages combatted?

The flintlock rifle used a spark made from flint and steel to ignite gunpowder that was loaded in the barrel of the gun. - The rate of firing was slow (could only fire a single shot at a time and took time to reload) - They were unreliable, especially in the rain The development of prepackaged ammunition and multiple-shot firearms

What is the difference between the magnaflux method and the acid etching method?

The magna flux method is designed to restore serial numbers that were imprinted on iron or steel - Nondestructive - Pretreatment with grinding tool to smooth surface - A mixture of fire iron fillings and light oil is applied while placing a magnet on the opposite side - The metal filings arrange themselves in the oil to provide a shadow of the original serial number The acid etching method is used on firearms that are made with both ferrous (iron) and nonferrous materials - Pretreatment with grinding tool to smooth surface - Fry's reagent is applied to the area of interest - It slowly dissolves away the extraneous scratches and markings revealing some of the numbers imprinted on the metal - Process is painstakingly slow and destructive

What is ballistics? What are three types of ballistics?

The study of a bullet in motion - Internal ballistics: events that transpire within the firearm - External ballistics: events that occur after the bullet leaves the barrel of the gun but before it strikes its target - Terminal ballistics: what happens when the bullet strikes its target