In order to leave powder burns on a body, how close would a gun have to be when fired? — Irene, Peachtree City, Ga.
Marshall Brain answered:
In order to understand the concept of a “powder burn”, it is helpful to look at what if coming out the barrel of a gun, besides the bullet, when the gun fires. These slow motion videos can help you to see what is happening:
What you are seeing is the flame of the burning gunpowder exiting the barrel, along with soot and unburned gunpowder particles. If the barrel of the gun is near the victim when the gun fires, the flame can actually burn the person’s clothing and skin. The gunpowder residue and soot also sticks to the person’s clothing and skin.
As you can see in the video, the actual flame front does not extend that far out of the barrel. The flame itself, or the extremely hot gases expelled with the flame, are what cause an actual powder burn. According to this page, actual burning is going to happen only when the barrel is very close to the victim. But powder residue can travel three feet or more, depending on the type of gun.