What substances are deposited on the rear of a gun due to blowback?

The correct answer is primer, lead, barium, and antimony because these substances are the primary components that can be found in the residue left on a firearm after it is discharged. When a gun is fired, the firing pin strikes the primer, igniting the gunpowder and causing a projectile to be propelled forward. This process generates a variety of byproducts, including the metallic residues from the primer.

Specifically, lead, barium, and antimony are common components of modern primers used in ammunition. Lead is often present in the primer material itself, while barium and antimony can be found alongside lead as additional ingredients or byproducts. When the gun operates, these materials can be expelled back toward the shooter or the environment, creating trace evidence that can be detected on the rear of the firearm or on the shooter’s hands and clothing.

The other substances listed do not accurately characterize the residues associated with blowback from a firearm. Smoke and dust might be present as environmental pollutants but are not specific residues from the operation of a gun. Plastic and glass fragments could potentially be involved in certain types of ammunition or firearms but are not the typical residues associated with primer discharge. Gunpowder residue alone does not encompass the full range of materials