List two reasons why striations on bullets fired from the same gun may vary slightly. The presence of grit and rust can alter the markings on bullets fired through the same barrel.
Why do bullets have different markings?
Fortunately for criminal investigators, the uniqueness of each firearm transfers to the cartridge case and bullet whenever the weapon is fired. … These differences can be used to identify or eliminate a weapon as being used in a crime, if a cartridge case or bullet is recovered at the crime scene.
How does a bullet receive striations when it is fired?
How does a bullet receive striations when it is fired? The bullet travels along the barrel and comes into contact with the spiral grooves along the barrel. These grooves cut into the side of the bullets and scratch its surface. … It causes the bullets to spiral as they exit the barrel.
Can it be determined whether these bullets were fired from the same gun?
A barrel will produce individual markings in addition to a bullet’s land and groove impressions as the bullet passes through, and it is these unique markings that an examiner evaluates to determine whether a given bullet was fired from a particular firearm.
How are striation markings or striations useful for comparing bullets?
How are striations useful for comparing bullets? The random distribution and irregularities of these markings are impossible to duplicate exactly in any two barrels. … The higher the gauge number, the smaller the barrel’s diameter.
Why are no two firearms even those of the same make and model the same?
Studies have shown that no two firearms, even those of the same make and model, will produce the same unique marks on fired bullets and cartridge cases. Manufacturing processes, use, and abuse leave surface characteristics within the firearm that cannot be exactly reproduced in other firearms.
Which type of firearm does not leave striations?
This lets the examiner compare the striations left on the fired bullets (2). Firearms are rifled during their manufacturing process, with the exception of smooth bore guns, such as shotguns.
How do they match bullets to guns?
The theory behind firearm identification is that microscopic striations and impressions left on bullets and cartridge cases are unique, reproducible, and therefore, like “ballistic fingerprints” that can be used to identify a gun. … A fired bullet with rifling impressions from the barrel of a gun (left).
What other unique markings are found on bullets after being fired?
This cartridge case shows the three distinct marks, or ‘signatures,’ impressed on its surface when it was fired by a gun: the firing pin impression (FP), the breech face impression (BF) and the ejector mark (EM).
Are ballistics accurate?
The test-firing results only scratch the surface of ballistic fingerprinting’s problems. The experts concluded it’s unknown whether cartridges fired after typical firearm break-in and wear can at all be matched to the cartridge fired when the gun was new. … “They are not permanently defined like fingerprints or DNA.”
What causes the bullet to shoot out of the casing?
The spark from the primer ignites the gunpowder. Gas converted from the burning powder rapidly expands in the cartridge. The expanding gas forces the bullet out of the cartridge and down the barrel with great speed.
Are bullets traceable?
Almost every bullet fired from a gun, can be traced back to that gun using a microscope. “When a bullet is fired from a firearm, when it travels through the barrel, the barrel leaves microscopic markings on the bullet that are unique to that specific firearm,” Jessica Wade, forensics firearms examiner, said.
What causes Chamber marks?
Most chamber marks occur after the cartridge is fired. Cartridge cases expand when fired pressing out against the walls of the chamber. When they are pulled out of the chamber, the sides of the cartridge case can be scratched.
In what part of the fired bullet and fired cartridge cases should the markings be placed?
Fired shotshell cases should be marked at the metallic base, where the base joins the plastic or fiber body. Plastic shotshells can be scribed in the thick plastic area near the base.
What is the process for comparing bullets and firearms evidence to a suspected weapon?
The science that deals with the scientific analysis of fired ammunition is called Ballistic Analysis, or simply Ballistics, which Oxford Dictionaries Online define as “the science of projectiles and firearms” or “the scientific study of the effects of being fired on a bullet, cartridge or gun.”
What are striation marks?
Striations are marks produced on the fracture surface that show the incremental growth of a fatigue crack. A striation marks the position of the crack tip at the time it was made. … The presence of striations is used in failure analysis as an indication that a fatigue crack has been growing.