firstgrouptwo


 * Gunpowder**, whether black powder or smokeless powder, is a substance that burns very rapidly, releasing gases that act as a propellant in firearms. Both forms of gunpowder are low explosives. As it burns, a subsonic deflagration wave is produced rather than the supersonic detonation wave which high explosives produce. As a result, pressures generated inside a gun are sufficient to propel a bullet, but not sufficient to destroy the barrel. At the same time, this makes gunpowder less suitable for shattering rock or fortifications, applications where high explosives are preferred.

Tara's Slides:

Gunpowder Residue
When the firing pin of a firearm strikes the primer of a cartridge the primer compound ignites sending a flame into the cartridge case. Gunpowder in the cartridge case starts to burn, causing it to change from a solid material to a gas. This change creates pressure within the cartridge, which in turn forces the bullet down the barrel and down range. Pressure building behind the bullet is released when the bullet exits the muzzle of the firearm. When the bullet exits the muzzle, pressure behind it blows the gunshot residues out of the firearm's barrel under high velocity. The residues are expelled from the barrel in a smoky cone shaped pattern.Gunshot residues emitted from the muzzle will travel out to distances of approximately 3 and 5 feet in most firearms but in some cases can travel even greater distances. At the 3-5 foot range the gunshot residues may only consist of a few trace particles and make determining the firing distance difficult if not impossible. As the firearm gets closer to its target the residue concentrations increase and the actual size or diameter to the pattern gets smaller. At around 18-24 inches most firearms will start to deposit considerable concentrations of gunshot residues that may or may not be visible to the eye. At distances of less than around 12 inches heavy concentrations of visible gunshot residues will normally be deposited.



Time-lapsed image showing a bullet exiting from the barrel. Streaks of burning gunpowder, smoke, and unburned particulate can be seen exiting the barrel as well.
The further gunshot residues travel from the muzzle, the broader and less concentrated the pattern becomes. Because the various elements included in gunshot residues are very small and lack mass they lose their energy rapidly.Gunshot residues can also be emitted from other areas of a firearm. As you can see in the above image, gunshot residue is escaping from the barrel/cylinder gap of the revolver.

=Visible gunshot residues around bullet entrance hole.= When the muzzle of the firearm gets next to or is in contact with the target, hot gases escaping from the muzzle at high velocity will typically rip, tear, shred, and/or melt the material of the target. A very intense deposit of gunshot residues will be found around the margins of a contact or near contact entrance hole.


 * Caylor's slides*

1.)Firing a weapon produces combustion of the primer and powder of the cartridge. The residue of the combustion products, or unburned primer or powder components, can be used to detect a fired cartridge.

2.)Residue may be found on the skin or clothing of the person who fired the gun, on an entrance wound of a victim, or on other target materials at the scene.

3.)Examination of clothing or other materials for traces of gunpowder or gunshot residue (GSR) provides an essential function during a criminal investigation

//**4.)G**//unshot residue distance standards are made by firing the firearm, using ammunition like that used in the actual case, into witness panels that consist of white pieces of cotton twill jean cloth. Seen below are three witness panels attached to a frame for display purposes. Normally only one panel is mounted and fired into at a time to prevent contamination.