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

253 Pages·2011·5.44 MB·English

by  Mark Denny

THEIR ARROWS WILL DARKEN THE SUN
THEIR ARROWS WILL DARKEN THE
SUN
The Evolution and Science of Ballistics
MARK DENNY
© 2011 The Johns Hopkins University Press All rights reserved. Published 2011
Printed in the United States of America on acid-free paper 9 8 7 6 5 4 3 2 1
The Johns Hopkins University Press
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Library of Congress Cataloging-in-Publication Data Denny, Mark, 1953– Their
arrows will darken the sun : the evolution and science of ballistics / Mark Denny.
p. cm.
Includes bibliographical references and index.
ISBN-13: 978-0-8018-9856-3 (hardcover : alk. paper) ISBN-10: 0-8018-9856-
0 (hardcover : alk. paper) ISBN-13: 978-0-80189857-0 (pbk. : alk. paper) ISBN-
10: 0-8018-9857-9 (pbk. : alk. paper) 1. Ballistics. 2. Trajectories (Mechanics).
3. Aerodynamics. I. Title.
UF820.D46 2011
623′.51—dc22 2010023459
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Contents
Acknowledgments
Introduction
I. BANG! Internal Ballistics
1. Before Gunpowder
2. Gunpowder Weapons
3. The Development of Modern Firearms: New Technical Challenges
II. WHIZZ! External Ballistics
4. Short-Range Trajectories: Elementary Aerodynamics
5. Long-Range Trajectories: Advanced Aerodynamics
6. New Technology, New Ballistics
III. THUD! Terminal Ballistics
7. Stopping the Target
Final Thoughts
Technical Notes
Glossary
Bibliography
Index
Acknowledgments
The process of publishing a book is one that takes time and the expertise of
many people besides the author. For permission to reproduce photos from his
collection, I am grateful to Bob Adams. For his excellent drawings of soldiers
from classical antiquity, I thank Johnny Shumate. At the Johns Hopkins
University Press, editor Trevor Lipscombe and art director Martha Sewall have
worked their usual magic, while copyeditor Carolyn Moser has turned my turgid
text into pristine prose—thank you all.
THEIR ARROWS WILL DARKEN THE SUN
Introduction
Ballistic science has been important to humans for as long as they have hunted
or waged war, but it is only over the past 250 years that the scientific discipline
of ballistics has matured from a craft art. A deep understanding of modern
ballistics theory requires specialized study over several years, and yet it holds a
fascination for nonspecialists. You most likely would not have picked up a book
explaining the science of thermodynamics, for example, though thermodynamics
is probably more important to our daily lives—so why a book on ballistics?
Maybe because of the popularity of hunting and target shooting. Ballistics and
guns go together like ham and eggs, although, as we will see, ballistics applies to
rocks, arrows, bombs, rockets, and flaming pianos as well as to bullets.
Why read a concise, semitechnical account of ballistics such as this one?
Maybe because you’re too busy earning a living to do a degree in ballistics but
are left unsatisfied by some of the Sunday comics explanations of how it all
works. You will not become a better shooter simply by reading this book: you
know better than I do about the practicalities of your hobby, be it benchrest, bow
hunting, or BBs. You will, however, gain a better understanding of ballistics
science—of why ballistic trajectories are the way they are.
Ballistics has a long history—I will share some of it with you—because, of
course, the development of firearms has greatly influenced the conduct and
outcome of wars. Much of our understanding of ballistics principles came
directly as a result of military development. Small arms and artillery weapons,
their propellants and projectiles, plus rockets and ballistic missiles from arrows
to ICBMs, have all evolved from simpler beginnings, over decades or centuries.
Improvements led to longer ranges, which, as we will see, brought in new
physics that required understanding (or, at least, accommodating) before
evolution could continue. New understanding led to yet longer ranges and
greater accuracy, and so the cycle repeated. It continues to this day.
The figures for gun ownership give a false impression of the worldwide
interest in hunting and shooting. There are 192 million privately owned firearms
in the United States and almost none in England, though both countries sport
many hunters and shooters. Outside of the armed forces, it is primarily hunters
and target shooters who are interested in ballistics. How many such folk are
there? According to the National Shooting Sports Foundation there are over 20
million active hunters in the United States (including 3.3 million bow hunters)
and over 23 million target shooters (6.6 million of them are archers). They shoot
with handguns, rifles, shotguns, air guns, longbows, and crossbows; they do it
standing up, sitting down, and lying prone. In England there are over 1,000
small-bore rifle and pistol clubs; around the world the story is the same. Target
shooting with small arms was one of the founding sports of the modern Olympic
Games, beginning in 1896, and archery was only four years behind.
Keen interest in a subject naturally leads many people to want to understand it
at a deeper level than they can glean from everyday experience. Hence, sailors
turn to aerodynamics to see how the wind fills their sails, and target shooters turn
to ballistics to learn the nuts and bolts of their hobby (or profession—many
military personnel need or want to know about ballistics). To cater to the large
public appetite for ballistics, there are literally thousands of publications. These
tend to fall into two broad categories which I can encapsulate with two made-up
book titles. The first is Splat! How to Build an Egg-Thrower in Your Garage!
and is generally aimed at a younger readership. Such books tend to be light on
technical details and heavy on fun. At the other extreme you will find titles such
as Spin Stabilization Data for .30-06 M2 Ball Ammunition: What Every
M1903A4 Rotating-Bolt Springfield Rifle Enthusiast Needs to Know. OK, so this
is hyperbole, but you get the point: books in this second category tend to be
hypertechnical and very specialized. While full of technical details, however,
they do not shed much light on the physical principles.
My book is aimed (an appropriate word) at the sparsely populated gulf
between these two extremes: I will share with you the physics, rather than the
engineering detail, that underlies ballistics (the why of ballistics, which I
mentioned a couple of paragraphs back). My purpose is to get across to you the
science of what is going on when you pull the trigger or release the arrow. We
will follow a projectile (arrow, bullet, artillery shell) as it arcs through the air and
see what effect it has upon a target.
You will not need a degree in engineering to follow the explanations, though I
hope that professional ballisticians can learn from this book. Math analysis is
included if you want it (but only if you want it) in a series of technical notes that
follow the main text. My purpose is to get across the many physical principles
that influence ballistics; to this end I will sacrifice details and perfect accuracy
(this is why I call my book “semitechnical”) because detail can cause confusion
and cloud understanding. Instead I will use simple—but not too simple—models
that convey the crux of an argument, without frills. If you crave the arcane
details that will make you a better shooter, or if you want practical help building
a toy ballista, then this is not the book for you. If you want to know why
ballistics works the way it does,1 then read on.
The scientific discipline of ballistics subdivides naturally into three parts, and
my book adopts this convention. First there is the brief launch phase of a
projectile. The object here is to provide the arrow, musket ball, or artillery round
with as much energy as possible and send it in the desired direction. Second is
the longer flight phase during which (until recently) the archer, shooter, or
gunner has had no influence over the projectile—physics takes full control.
Finally the terminal phase: our spear, sniper bullet, or mortar round hits
something and penetrates, fragments, or explodes. In this book you will discover
accessible explanations of all three ballistic phases, with or without math.
Math analysis is restricted to a series of technical notes at the end of the book
because equations get in the way of readability. You may choose to omit the
math analysis completely without missing out on any of the essential concepts,
which require words to convey. If, on the other hand, you crave detail, there is
enough of it in the technical notes for you to derive all the results shown in the
physical models of ballistics phenomena that I construct.2 So, whatever your
technical requirement and whatever your interest in this engrossing subject, there
is much in the pages to follow that will inform, stimulate, and amaze you.
A final word about units and notation. As a physicist I naturally incline to the
metric system, and so the detailed calculations that you will encounter in the
technical notes, if you choose to do so, use dimensions of meters, kilograms, and
seconds, plus their derivative units of newtons, joules, kilowatts, and so on.
Much of the popular ballistics literature retains the old English system of
measurement, and so in the main text I will occasionally use both systems, as in
“a 32-pounder long gun from the Age of Sail had a maximum range of 2,600
yards (2,400 m).” Some modern firearm calibers are quoted in inches and others
in millimeters; I will also freely mix these units, instead of converting. Common
parlance refers to bullet velocity when, to a physicist, it should sometimes be
speed. I will generally try to distinguish between these terms.