In the 15th century, rifling, the process of making grooves in gun barrels that imparts a spin to the projectile for increased accuracy and range, first appeared.

Fig 3. is a color photograph of the micro-imprint made on the primer of a cartridge made by the firing pin of a handgun. The statute was supported by law enforcement because it can help deter or solve crime.

This is a major step forward but has drawbacks as well.

Because of this rifling, bullets fired from rifled weapons acquire a distinct signature of grooves, scratches, and indentations which are of value for matching a fired projectile to a firearm. It was Alexandre Lacassagne who, in the early 20th century, was the first scientist to try to match an individual bullet to a gun barrel.

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Fig 2a. shows a cross section view of the barrel, showing 201 the lands, or the original smooth surface of the barrel, and 202 the grooves, or rifling, that have been machined into the barrel.

Fig 2b. shows how the bearing surface of the bullet is forced into the rifling as the bullet passes through it.

Fig 2c. shows how lands and grooves, 201 and 202, are a negative impression of the rifling.

The first use of ballistic identification used as evidence can be traced back to England in 1835, when the unique markings on a bullet taken from a victim were matched with a bullet mold belonging to the suspect. When confronted with the damning evidence, ​the suspect confessed to the crime.​

If investigators are lucky enough to recover a weapon, bullets can be test fired and the lands and grooves from the test rounds compared with the bullet from the crime scene. This comparison can be used to confirm if a recovered bullet was fired from that gun or not. If no weapon is found, or if the test fired rounds do not match the crime scene bullet, that's all the investigators have. A bullet.

In 2013, California became the first state to bar retailers from selling new models of semiautomatic handguns not equipped to imprint the weapon’s make, model and serial number on the cartridge when a bullet is fired.

Stamps wear out and disappear. As a gun is fired the chamber and associated parts are subjected to immense levels of pressure and friction.

Everything is in a constant process of erosion and decay. The characters on the firing pin are no different. The imprint made on round number one will be bright and easy to read, but over time these characters will chip, break or become filled with the softer metal of the struck primers.

Micro-stamping is a great tool for semi-automatic firearms, but what about revolvers. While semi-automatic weapons spit their spent casings everywhere, revolvers retain those casings and keep them with the gun. So instead of a crime scene littered with finely stamped casings, there’s nothing.

Whether it’s a revolver, a plastic bag over the gun, or even just a criminal that takes the time to police their brass, it only takes a little bit of effort to deprive the police of the evidence that micro-stamping would have provided.

At the present, the micro-stamping statute is on the books, but manufacturers have yet to overcome production problems so no weapons are being produced.

physical contact with the inside of the barrel during expulsion. The cannelure 103, if the bullet has one, is designed to hold the bullet firmly in the casing until maximum pressure has built up within the cartridge on firing. The lands 104, and grooves 105, are carved into the bullet by the rifling in the guns’ barrel. The base of the bullet is 106.

Fig 1. is a color photograph of a recovered bullet 101 showing the mushrooming to the nose caused by impact. The bearing surface 102 is where the bullet is in

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​A Giant Step Forward In Forensic Science