Breech face marks- These marks come from the area surrounding the firing pin of the gun. After the cartridge powder is ignited by the firing pin striking the primer cup, tremendous pressure is exerted in the chamber of the weapon, forcing the back of the cartridge case against the breech face of the weapon.
What do breech marks look like?
Breech marks can also show no obvious pattern. They may have a stippled or mottled appearance as seen below. Now back to ejector marks. Ejector marks are sometimes created when cartridges or cartridge cases are ejected from the action of a firearm.
What causes breech face marks in the cartridge head quizlet?
are indentations created when the firing pin of a firearm strikes the primer of centerfire cartridge case or the rim of a rimfire cartridge case. When the head or base of the cartridge case moves rearward, it strikes what is called the breech face of the firearm.
How breech face marks and aperture shear marks are imparted on a cartridge case?
Please describe how breech face marks and aperture shear marks are imparted on a cartridge case. aperture shear marks are imparted Striated toolmarks caused by the rough margins of a firing pinhole (aperture) scraping the primer metal during unlocking of the breech of a firearm.
What material is used the most when producing bullets Why?
Lead is Malleable When compared to other materials, lead offers a higher density and less rebound, making it ideal for shaping and manufacturing into high-quality ammunition.
What are extractor and ejector marks and what kind of weapons do these marks come from?
Extractor and ejector marks are produced when the cartridge case is mechanically extracted from the chamber and ejected and are visible as fine striations and gouged impressions on the rim and head of the case. Casings contain information about the type of ammunition, stamped onto the base of the cartridge.
What is the difference between ejector and extractor?
The extractor mechanism removes a cartridge from the chamber, while the ejector throws the cartridge away once it is extracted.
What causes ejector marks on brass?
Ejector marks are signs of over pressure, tread carefully.
What are chambering marks?
The chamber is known to imprint its surface striations irregularities on the cartridge case, in what are called chamber marks, due to the pressure produced when shooting. Such chamber marks are even more pronounced on substandard firearms or when firing a from an undersized chamber.
How do bullets stay in the chamber?
Because the projectile (the bullet) is actually held into the case by the tension on the case mouth (the place where the bullet fits in the case to form a cartridge). The bullet is held in the case by spring tension exerted on the malleable brass of the case mouth.
What causes Chamber marks?
One of the most common striated action marks are called chamber marks. Roughness in the chamber of a firearm can scratch the outer walls of a cartridge case when loaded and removed from the chamber. Most chamber marks occur after the cartridge is fired.
What three types of marks are left on the casing after a gun is 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).
What’s the difference between a 357 and a 357 magnum?
Energy Comparison: 357 Mag and 357 Sig 357 Magnum often comes with larger projectiles, which would give it an advantage for muzzle energy. 357 SIG. The larger Magnum cartridge has lower speeds but a muzzle energy of 539 foot-pounds, while the . 357 SIG, a faster cartridge, has only 506 foot-pounds of muzzle energy.
What is the biggest problem in making an identification in bullets?
One of the biggest problems in making an identification is that few evidence bullets are submitted intact. Most are badly distorted, wiped and/or fragmented.
What are the bullets principles of identification?
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). To help stabilize the flightpath of a bullet, manufacturers cut spiral grooves into the gun barrel.
How are bullets marked for identification?
Bullets are marked on the nose at the 12 o’clock barrel position (called “index”, “witness”, or “reference” marks). Consecutive test bullets are then fired into a water tank, recovered, and juxtaposed with a comparison microscope to compare test bullets with the recovered evidence.
What are some characteristics used to identify and compare bullets?
On bullets, the class characteristics are the rifling specifications of the barrel from which the bullet was fired. These include caliber, number of lands and grooves, direction of twist of the lands and grooves, and widths of the lands and grooves.
