The reference firearms collection dates back to 1933 and contains more than 7,000 types of firearms. “We try to have one example of every type of firearm—make, model, finish, serial number configuration, you name it,” says John Webb, a firearms examiner. “We want to have an example of each kind. So when a firearm comes in for disposition, if anything about that firearm is different from what we already have in the collection, we’ll add it to the collection.”
A fired bullet is observed on a comparison microscope to reveal the lands and grooves and unique microscopic markings that were carved into the bullet as it travel through a gun barrel. The microscope allows an examiner to compare two bullets or cartridge cases simultaneously, under the same field of view, focal plane, and lighting conditions.