From Hellhound On His Trail: The Electrifying Account of the Largest Manhunt In American History, by Hampton Sides (Knopf Doubleday, 2010), Kindle pp. 240-241:
ON ANOTHER FLOOR of the FBI Crime Lab, Robert A. Frazier spent the morning examining and test-firing the Remington Gamemaster after it had been dusted for fingerprints. A ferociously methodical man with nearly three decades’ experience, Frazier was the chief of the FBI’s Firearms Identification Unit, where a team of ballistics experts worked around the clock in what was widely considered the world’s preeminent weapons-testing facility. Here technicians fired rifles into water recovery tanks, examined bullet fragments and firearms components under high-powered microscopes, and subjected objects to arcane tests to detect such things as the presence of gunpowder and lead.
Within a few hours, Frazier and his team had made a long list of important preliminary findings.
First, the projectile which Dr. Francisco had extracted from Martin Luther King’s body only a few hours earlier was a .30-caliber metal-jacketed, soft-nosed bullet made by the Remington-Peters Company—identical in manufacture to the unused Remington-Peters .30-06 rounds found in the ammo box that was part of the bundle.
Second, Frazier was able to ascertain the kind of barrel from which the bullet was fired. The barrels of modern firearms are “rifled” with spiral grooves that are designed to give bullets a rapid spinning motion for stability during flight. The raised portions between the grooves are known as lands. The number, width, and direction of twist of the lands and grooves are called the class characteristics of a barrel, and are common to all firearms of a given model and manufacture. Frazier determined that the bullet that killed King had been fired from a barrel “rifled with six lands and grooves, right twist,” and that the Gamemaster, analyzed under a microscope in his laboratory, exhibited the same land-and-groove pattern.
Third, the spent cartridge that Special Agent Jensen had removed from the chamber had been fired in the same Gamemaster rifle, as evidenced by a tiny “extractor mark” Frazier found imprinted on the metal casing. At the base of this spent cartridge case, Frazier discovered a head stamp that said, “R-P .30-06 SPRG,” indicating that it was a Remington-Peters round of the same caliber as the ammunition found in the ammo box.
Frazier concluded, based on the “physical characteristics of the rifling impressions” as well as other factors, that the bullet removed from King’s body could have been fired from the Remington Gamemaster. However, he could not say with scientific certainty that the bullet came from this rifle, “to the exclusion of all other rifles.” This was because the bullet, as he described it in his report, “had been distorted due to mutilation” as it struck hard bone while passing through King’s body.
Frazier knew that the mechanical components of individual firearms (such as the firing pin and breech face) have distinctive microscopic traits that can engrave telltale markings on bullets. The tiny striations often found on fired bullets are known as individual identifying characteristics and are, in effect, the ballistics equivalent of a fingerprint. Frazier had hoped the bullet that killed King would exhibit these telltale markings, but it didn’t: the round, having been chipped, dented, warped, and broken into several discrete parts, was missing the critical information.
Far Outliers 