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304 North Cardinal St.
Dorchester Center, MA 02124
Which two elements would be detected on the hands of an individual who has recently fired a weapon? Bullet will be made to spin and have a true and accurate course on leaving the barrel. Two elements detected on the hands of an individual who has recently fired a weapon are: A. Antimony and iron.
Which of the following makes the final determination about whether two bullets were fired from the same gun? NIBIN makes the final determination about whether or not two bullets were fired by the same gun. Distance determination is usually based on the distribution of powder patterns or the spread of a shot pattern.
What technique is used to detect GSR? Gunshot residue (GSR) analysis is a standard method to determine if a firearm has been used. Particles for GSR analysis typically range from 0.5 to 10 microns. Often the primer particles containing lead (Pb), barium (Ba) and antimony (Sb) are detected and analyzed using EDS in a scanning electron microscope.
Which of the following are forensically useful markings that can be found on spent shell casings? In addition to examining lands and grooves on a bullet, investigators can examine firing pin marks, breechblock marks, and extractor and ejector marks on a spent cartridge casing to match evidence at a crime scene with a specific firearm.
Distinctive markings of shells and cartridges can be made by the: Extractor and ejector mechanism.
To evaluate old bullets, ballistics experts rely on the same basic techniques used at police labs. Most clues are found in two types of tiny markings, called class and individual characteristics. By looking for the bullet caliber and “rifling” marks, experts can identify the type of gun used.
To match a bullet to a particular firearm the examiner looks for two criteria using comparison microscopy: class characteristics and individual characteristics. Class characteristics are measurable features of a specimen that indicate a restricted group source.
The stubs of the gunshot residue kits are analyzed for constituents of gunshot residue, namely the elements lead (Pb), antimony (Sb) and barium (Ba). These three elements originate from the primer of most firearm cartridges.
These elements are considered heavy metals. Additionally, lead, barium, and antimony are the three key elements found in the primer that characterize GSR. This study aimed to develop a method to differentiate among the inorganic components found in different types of ammunition used in a variety of firearms.
Gunshot Residue Tests
Detection of GSR has two primary objectives: (1) determining if an individual fired or handled a recently discharged firearm or if a surface was in close proximity to a weapon during discharge; and (2) analyzing the pattern of GSR for the purpose of determining the muzzle-to-target distance.
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).
Some of the class characteristics found on a fired bullet are (1) the caliber of the bullet (diameter), (2) the number of lands and grooves, (3) the twist of the rifling (left or right), and (4) the widths of the land and groove impressions.
mpressions are made on the bottom of the cartridge by the firing pin as it strikes to fire. Depending on the firearm and type of cartridge used, these marks can appear on the rim or the center of the used cartridge.
Impressed marks are created on cartridge cases when it impacts the tool (again, the firearm) with adequate velocity or pressure to leave an impressed or indented mark. Cartridge cases are compared to fired standards from a firearm using a comparison microscope.
General Rifling Characteristics
These include the caliber (bore diameter) of the barrel, the number and dimension of the grooved impressions inside a gun barrel, and the direction of the twist of these rifling grooves (clockwise or counterclockwise).
There are three basic malfunctions that can be attributed to ammunition specifically: the misfire, the hangfire, and the squib load.
When a bullet is fired from a gun, the gun leaves microscopic marks on the bullet and cartridge case. The examiner will then assess how similar the two sets of marks are and determine if the bullets are likely to have been fired from the same gun or different guns. Cartridge cases are compared in the same way.
Every bullet can be matched to a particular weapon through comparing striation marks. Striations are made through a process called rifling. With each impression, microscope, marking are made within the bore to make each gun have a unique set of striations marks.
Forensic firearm examination is the forensic process of examining the characteristics of firearms or bullets left behind at a crime scene. Specialists in this field are tasked with linking bullets to weapons and weapons to individuals.
Gun shot residue is tested by lifting samples off a defendant’s hands or clothing and then testing to see if the lifts contain a fused particle of barium, antimony, and lead, which are known to be present in GSR.
Gunshot residue contains burned particles (potassium nitrite) and some unburned particles (potassium nitrate), and for decades criminal investigators collected these particles by applying melted paraffin wax to a subject’s hands.
Finding and viewing primer GSR particles require a high-powered microscope, such as an SEM. Gunshot residue particles can be removed easily from the surfaces they land on.
Sodium Rhodizonate Test
This colorimetric test analyzes for the presence of barium and/or lead, which are constituents of the bullet primer1 and yields a red-brown color when either lead or barium is present.
Cartridge cases are most commonly made of brass, although steel is also widely used, and cases for shotgun pellets are made of brass and cardboard.
The cartridge case, bullet, bullet coating, and metal jacket contain specific elements that can be detected. Virtually all cartridge cases are made of brass (70% copper and 30% zinc). A few have a nickel coating. Primer cases are of similar composition (Cu-Zn).