The crime lab has received a fired bullet and a discharged cartridge case from the scene of a shooting. This evidence is submitted to the crime lab for examination. Several weeks later, the police confiscated a semi-automatic pistol from a suspect in the shooting. A semi-automatic pistol is a specific type of handgun with a single barrel and single chamber. These types of guns load a new cartridge into the chamber after each shot. Every time the trigger is pulled, one round is shot from a semi-automatic. Other types of hand guns have multiple chambers and a single barrel, or multiple chambers and multiple barrels, but also have one trigger pull to one round fired. However, these are not classified as semi-automatic pistols. .
The scientific method is the "tried and true" way to determine the truths from the untruths when trying to determine an outcome or a solution. Very simply, the scientific method consists of the following:.
1. Observe something.
2. Come up with a hypothesis, or tentative description using the observation .
3. Make a prediction.
4. Test the prediction either by further observations or experiments, then modify the hypothesis.
if necessary.
5. Keep repeating #3 and #4 until the theory and the experiments match.
The theory becomes the framework that explains the observations. In other words, the theory becomes the answer. This can be used by a firearms examiner to provide facts and opinions relating to firearms examinations. The reason is that studies have shown that firearms each will produce totally different marks on bullets and cartridge cases. If the firearms examiner has a questioned firearm, therefore, he or she can use it to determine if that firearm was probably the one used to fire the bullet or cartridge case in question.
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All firearms identifications start with class characteristics which means those common to a group or family of items. In this case it might be those bullets that could be fired from a 9mm semi-automatic handgun and the marks or rifling pattern in the barrel of the firearm.
