Their Arrows Will Darken the Sun: The Evolution and Science of Ballistics

Glossary

Glossary Ballistics is a widespread and ancient science and consequently has evolved, over the years, a language of its own. A comprehensive glossary would therefore be as long as a dictionary. Here I include only ballistics terms that are used in the book, and even then I will be selective, omitting words of peripheral or of obvious and unambiguous meaning. Thus, for example, you will find drag force but not gravitational force, and smart bomb but not bomb. Angle of attack. The angle between an airfoil (such as a bullet) and the wind direction. Archer's paradox. An apparent paradox concerning the flight of a longbow arrow as it passes the bow handle. Geometry suggests that the arrow flight should be deflected, but physics ensures that it is not. Arquebus. An early shouldered firearm, a muzzle-loading smoothbore with a wheel-lock firing system; ancestor of the musket. Artillery. Cannon; the ordnance branch of an army. Assault rifle. A military rifle capable of both automatic and semiautomatic fire, of intermediate power, usually with a large magazine. Assegai. A throwing spear associated with the Zulus. Atmospheric attenuation. The exponential reduction in the density of air with height above the earth's surface. Automatic. A firearm that reloads and fires rapidly and repeatedly until the trigger is released. Ball. Spherical musket ammunition. The name was retained even for nonspherical ammunition such as the Minie bullet and provides us with the term "round." Ballistic coefficient. The sectional density of a bullet divided by its form factor—a complicated and outdated, but popular, measure of bullet "slipperiness ," or ability to pierce the air. Ballistic gelatin. A substance used as a substitute for human flesh in investigations of the effects of bullet penetration. 208 Glossary Ballistic pendulum. An eighteenth-century invention for measuring the speed of a bullet, consisting of a block of known mass (into which the bullet is fired) suspended from two rods that are free to rotate. Bullet speed can be calculated from the measured blockdeflection. Ballistics. The study of the dynamics of unguided (i.e., free-flying) projectiles. Barrel. The tube through which a bullet travels when fired from a gun. The barrel determines bullet direction and spin. Base bleed. Gas jet emission from the base of an artillery shell, which reduces tail drag by filling in the partial vacuum that forms behind the base. Battery. A tactical unit of several artillery weapons and their crews, used for combined action. Beamrider. Aguided missile that flies along the direction of a guidance beam that is pointed at the missile target. Benchrest. A tablelike support for a target rifle. Benchrest shooters are motivated chiefly by maximizing accuracy at long range, and thus customize their rifle and ammunition to attain this end. Berdan. Acartridge primer system popular outside the United States. Slightly less expensive to produce than the rival Boxer system but not reusable. Black powder. A low explosive used for centuries as the propulsive charge for firearms, consisting of a fine powder that is a mixture of charcoal, sulfur, and potassium nitrate. Superseded by smokeless powder. Blowback. An automatic pistol mechanism powered by recoil and gas pressure . Boat tail. A tapered bullet shape that reduces tail drag. Bodkin. An armor-piercing arrowhead, bullet-shaped rather than flat. Bolt. A crossbow arrow, considerably shorter than a longbow arrow. Bombard. An ancient type of cannon with a short barrel and large caliber that fired stone or iron shot in a high-angle trajectory.Ancient equivalentof the mortar. Bombardier. The crew member on a bomber airplane responsible for bomb aiming and release. Originally, any member of a gun crew. Bore. The hollow part of a gun barrel. Bourrelet. The largest-diameter parts of an artillery shell, excluding the driving band. Boxer. The cartridge primer system most used within the United States, favored because it can readily be reused. See also Berdan. Breech. The rear part of the barrel into which the cartridge is inserted. Breech loader. A gun or small arm which is loaded via the breech. Brisance. A measure of the rapidity of an explosion or deflagration. Bullpup. A modern assault rifle design in which the action and the magazine Glossary 209 are behind the trigger, so that part of the barrel is within the stock. This design shortens the weapon without shortening the barrel. Caisson. A two-wheeled wagon containing ammunition boxes, attached to the limber of a horse-drawn artillery piece...