This would comport with the first step in the scientific examination. .
As for the found or questioned cartridge case, the class would include those with the same marks, firing pin impressions, and other things. If either the bullet or the cartridge case had dissimilar class characteristics, they would then be eliminated, which follows along with the scientific methodology. .
If the bullet or the cartridge case class characteristics are similar, then a more thorough examination would take place to determine individual characteristics. These are marks made by different irregularities of the surfaces. They can be made by the maker, by use of the firearm, damage or other changes. They would be unique to the firearm and would distinguish it from every other one. The movement of the ammunition components through the firearms transfers marks onto the bullet or cartridge case and makes possible firearms identification. Bullets, of course, travel through the barrel with a sort of a twisting motion making marks called lands and grooves on the bullets. These marks are unique. .
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As with bullets, cartridge cases pick up marks, too, but in a different way. When cartridges are put into the firearm, the possibility of a tool mark exists. It does not even have to be fired. But, striated marks can be on cartridge cases that come in contact with various parts of the firearm. .
Sometimes making comparisons of these marks is difficult to impossible because of the conditions of the bullets or cartridge cases that are recovered. Many times they can be badly distorted, or fragmented. However, fragments can sometimes retain some of the marks used for identification purposes. The smaller and more damaged the questioned fragment, of course, the more difficult the identification would be. .
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One of the first events concerning firearms identification occurred in 1835 in London England. A person was shot and died, and one of his household staff was accused of the shooting.