That will depend on the type of gun (revolver versus rifle, etc) how many times it was fired, and what the hands were exposed to after the firing. It is typically measured in days.
Gun Shot Residue
GSR is the abbreviation for Gun Shot residue. It is a forensic test for materials left on the skin from a close range firearm wound.
Residue tests can detect gunshot residue on a person's hands, clothing, or skin, indicating recent contact with firearms. Additionally, forensic analysis can link ballistic evidence such as bullet casings or bullets to a specific gun. CCTV footage or eyewitness accounts may also help establish if someone shot a gun at a specific time and place.
The firing squad is a form of Death Penalty, so people were shot by the firing squad for committing crimes for which death was the sentence.
Two. One from the firing squad who had a conscience shot and the second from the follow up.
Gun Shot Residue
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GSR - gunshot residue
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lead