“Today, it may be set down as a scientific fact, and a postwar discovery now first made public, that no two revolvers or pistols ever leave precisely the same marks upon a bullet, and that it now is possible and practicable to link the bullet to the weapon in virtually every instance.” This is a quote from W.S. Stout about the science of ballistics in 1925, when firearm identification had began to be considered. In the early 19th century, firearms and bullets began to be mass produced and rifling patterns were made uniform by manufacturers. Rifling patterns inside the barrels of guns were necessary at this time because if a firearms maker or law enforcement officer had to determine if a bullet from a crime scene was from a certain gun, they could determine if the patterns were too large or skewed right or left. The rifling pattern in a barrel can be determined by counting the grooves around a bullet and checking the twist patterns. To determine the twist pattern on a bullet, you hold the nose of the bullet away from you and look at the way the impressions are traveling.This is one of the bullets that we have collected from November 11th, 2017 that clearly shows the rifling pattern is skewed to the right.Firearm identification appealed to the public after the publishing of two articles called “Fingerprinting Bullets” in the Saturday Evening Post, a magazine produced only six times a year. These articles were created from the works of Charles E. Waite, who was a legal investigator in the Charles Stielow case. Charles Stielow was convicted and sentenced to death for murder in New York in 1915, which was based on a clumsy firearms identification testimony. Waite investigated this testimony, and came to the conclusion that Stielow’s revolver couldn’t have fired the bullets that killed Charles Phelps and Mrs. Wolcott. After his investigation success, he went on to visit firearm companies to expand his knowledge on how firearms and ammunition were manufactured. Waite joined with Major Calvin Goddard, an officer in the Ordnance Corps, chemist Philip Gravelle, and physicist John Fisher to form a private Bureau of Forensic Ballistics in New York City. These four men were among the first experts to study firearms identification, and they all had contributed to the knowledge of firearms that we have today. Gravelle created a comparison microscope to be able to look at the crime scene evidence while looking at the bullet fired from a recovered weapon. This microscope had been the base for modern examiners’ equipment and methods. Goddard became famous through his work in the Sacco and Vanzetti case in 1927 and the St. Valentine’s Day Massacre in Chicago in 1929. In the Sacco and Vanzetti case, Goddard test fired a bullet from Sacco’s gun into a mass of cotton and then used Gravelle’s comparison microscope to seek the differences between these bullets.The first two bullets that he had shot didn’t match, but the third one did, which showed that random variation in marking is caused by many differences in expansion, pressure, and angles. Defense experts agreed upon the investigation, and Sacco and Vanzetti were executed. In the St. Valentine’s Massacre in Chicago, Goddard examined various fired bullets, shotgun pellets, and spent cartridge cases and came to the conclusion that one 12-gauge shotgun and two Thompson submachine guns were used in the murder. Goddard then matched the bullets to the guns found in a suspect’s home, thereby finding the killer.With these investigations of bullet theory and firearm identification, metal cartridges were becoming popular in the mid-19th century. These cartridges were a huge step from pouring gunpowder into the barrel, which was time consuming, and hoping that the gunpowder would ignite. The cartridge case contained a percussion cap in its base, and when the firing pin struck the primer, the gunpowder would ignite. The cartridge case would expanded from the explosive gases that were produced by the firing pin, and was pressed against the breech (back of the chamber) and the firing pin as the bullet was pushed down the barrel. The cartridge was then extracted or ejected from the rifle, shotgun, or semi-automatic pistol after each shot so that a new round can be loaded and fired. Revolvers were the only gun that people could manually remove their cartridges from because the cylinder rotates after each shot, keeping them unharmed and safe in crime from any investigators like Goddard. With this new moisture-resistant unit derived from post-American Civil War bullets, experts came to the conclusion that firing pin marks and breech marks can be used to help match spent cartridge to a specific firearm along with rifling patterns. Goddard and his Bureau of Forensic Ballistics team went on to training the first firearms identification expert at the FBI laboratory in 1932, which is now one of the largest employers and trainers of firearms. With the publication of three major firearms identification treatises in 1934 and 1935, this firearms identification field had become accepted by law enforcement in the United States, the United Kingdom, and Europe. The techniques pioneered by Goddard and his peers are still in use by modern firearms examiners, and now with technology, firearms examiners can use digital imaging and databases to search for matches for crime scene evidence quicker.