Gunshot residue
Crime scene specialists collect GSR from people and objects when there is reason to believe it may be there. The collected samples are then taken to a laboratory where they are examined. Forensic scientists can also use GSR residue to determine the distance between the barrel of the fired weapon and the target. The farther from the weapon the less the gunshot residue. Collection of GSR is time sensitive in many cases. After 4 to 8 hours it may wear off people's hands. It can remain for longer periods on a dead body or other objects. A number of advancements have been made in gunshot residue examinations in recent years. One improvement is in the use of scanning electron microscopes.