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Basic Ballistics

A Short Tutorial

By Monica BennettPublished 6 years ago 3 min read
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Ballistics is a science that encompasses more than you think it does. There are several disciplines including internal ballistics which deals with the actual propulsion of a bullet through a gun, while external ballistics is the analyzing of the bullet's path through the air. There are several things that can influence a bullet's flight path, such as wind, weather, and air drag. Impact of a bullet is categorized as terminal ballistics. This leads to analyzing the angle and depth of wounds and impacts into walls or ceilings and various objects which have been struck. In April of 1925, Calvin Goddard established the Bureau of Forensic Ballistics in New York City with C. E. Waite, Philip O. Gravelle, and John H. Fisher. The biggest advance in ballistics was the invention, by Gravelle, of the comparison microscope. This device enabled scientists to see a crime scene bullet at the same time as a bullet test-fired from a suspect's gun.

Handguns and rifles, almost universally, have lands and grooves called rifling. It puts a spin on the bullet so it flies in a relatively straight path in much the same way you put spin on a football when throwing it. Shotguns do not have rifling, and neither do zip guns, which are homemade guns. The manufacturing of a gun involves drilling the bore into a solid piece of steel. The action of the drill imparts characteristics called striations in the bore, even two guns made in succession. These striation marks are what the investigator compares for a match. The arrangement of grooves and lands which impress the bullet as well can give information on the make of the gun. Some twist to the left, others to the right, and at least one is polygonal. The number of grooves changes as well.

While revolvers are still in use today, the semi-automatic handgun is the most common weapon used in crimes. A semi-automatic loads the bullet into the chamber from the magazine, extracts the shell, and then the ejector expells the shell, usually to the right of the shooter. Evidence can be gotten from the shell, and the perpetrator has to either gather them up or leave them behind. These shells can bounce, roll, or ping off objects and can be very difficult to find. The shells remain in a revolver. A revolver has to be cocked each time you shoot. A semi-automatic fires every time you pull the trigger without having to be cocked. An automatic weapon keeps firing over and over until you take your finger off the trigger. They are expensive to buy and register and are highly regulated, which makes them rare at crime scenes. AR57 does not stand for assault rifle. It stands for ArmaLite Rifle; ArmaLite is the manufacturer.

Getting the terminology right is important. A cartridge, or shell, is different from a bullet. The bullet is just the lead bulb in a cartridge. The bullet separates from the cartridge when it is fired. Shotgun ammunition is very different from a bulletin that it fires a shell with tiny ball bearings, in various sizes. A magazine and a clip are not the same things. A clip is a device that holds bullets together for insertion into a magazine. A clip has no springs, a magazine does.

Shotgun Shell and Bullet Cartridge

Gauge and caliber are different terms as well. Shotguns are delineated by gauge. The higher the number, the smaller the gun. A 12 gauge shotgun is bigger than a 29 gauge. A 12 gauge will take a 1/12th-pound lead ball. Confusing, but it has to do with cannon fire. Caliber is the measurement of the internal barrel of a gun from land to land. Caliber is given in either part of an inch or millimeters. So a .45 is .45 of an inch. Evidence from a shotgun shell may be very difficult to ascertain. Nothing is left that's traceable except for the empty shell. However, tool markings on the base of the shell might aide an investigator.

There is no such thing as a silencer outside of Hollywood. There is no way to silence a gun, as each bullet expended is a controlled explosion. There are suppressors which help contain the gases released during firing, but they do not silence the gun. Another fallacy is the "cop killer" bullet. Also known as KTW's, these bullets are coated with Teflon. Teflon was used to protect the barrel from hard metal cartridges. They do not penetrate the Kevlar of bulletproof armor any more easily than any other bullet. A rifle gunshot will.

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About the Creator

Monica Bennett

I am a retired high school and college teacher. I have taught forensics, biology, chemistry, ecology, and Earth science.. Long Island has been my home for 60 years.

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